1 ======================== 1 ========================
2 ftrace - Function Tracer 2 ftrace - Function Tracer
3 ======================== 3 ========================
4 4
5 Copyright 2008 Red Hat Inc. 5 Copyright 2008 Red Hat Inc.
6 6
7 :Author: Steven Rostedt <srostedt@redhat.com> 7 :Author: Steven Rostedt <srostedt@redhat.com>
8 :License: The GNU Free Documentation License, 8 :License: The GNU Free Documentation License, Version 1.2
9 (dual licensed under the GPL v2) 9 (dual licensed under the GPL v2)
10 :Original Reviewers: Elias Oltmanns, Randy Du 10 :Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
11 John Kacur, and David Te 11 John Kacur, and David Teigland.
12 12
13 - Written for: 2.6.28-rc2 13 - Written for: 2.6.28-rc2
14 - Updated for: 3.10 14 - Updated for: 3.10
15 - Updated for: 4.13 - Copyright 2017 VMware In 15 - Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt
16 - Converted to rst format - Changbin Du <changb 16 - Converted to rst format - Changbin Du <changbin.du@intel.com>
17 17
18 Introduction 18 Introduction
19 ------------ 19 ------------
20 20
21 Ftrace is an internal tracer designed to help 21 Ftrace is an internal tracer designed to help out developers and
22 designers of systems to find what is going on 22 designers of systems to find what is going on inside the kernel.
23 It can be used for debugging or analyzing late 23 It can be used for debugging or analyzing latencies and
24 performance issues that take place outside of 24 performance issues that take place outside of user-space.
25 25
26 Although ftrace is typically considered the fu 26 Although ftrace is typically considered the function tracer, it
27 is really a framework of several assorted trac 27 is really a framework of several assorted tracing utilities.
28 There's latency tracing to examine what occurs 28 There's latency tracing to examine what occurs between interrupts
29 disabled and enabled, as well as for preemptio 29 disabled and enabled, as well as for preemption and from a time
30 a task is woken to the task is actually schedu 30 a task is woken to the task is actually scheduled in.
31 31
32 One of the most common uses of ftrace is the e 32 One of the most common uses of ftrace is the event tracing.
33 Throughout the kernel is hundreds of static ev 33 Throughout the kernel is hundreds of static event points that
34 can be enabled via the tracefs file system to 34 can be enabled via the tracefs file system to see what is
35 going on in certain parts of the kernel. 35 going on in certain parts of the kernel.
36 36
37 See events.rst for more information. !! 37 See events.txt for more information.
38 38
39 39
40 Implementation Details 40 Implementation Details
41 ---------------------- 41 ----------------------
42 42
43 See Documentation/trace/ftrace-design.rst for !! 43 See :doc:`ftrace-design` for details for arch porters and such.
44 44
45 45
46 The File System 46 The File System
47 --------------- 47 ---------------
48 48
49 Ftrace uses the tracefs file system to hold th 49 Ftrace uses the tracefs file system to hold the control files as
50 well as the files to display output. 50 well as the files to display output.
51 51
52 When tracefs is configured into the kernel (wh 52 When tracefs is configured into the kernel (which selecting any ftrace
53 option will do) the directory /sys/kernel/trac 53 option will do) the directory /sys/kernel/tracing will be created. To mount
54 this directory, you can add to your /etc/fstab 54 this directory, you can add to your /etc/fstab file::
55 55
56 tracefs /sys/kernel/tracing trace 56 tracefs /sys/kernel/tracing tracefs defaults 0 0
57 57
58 Or you can mount it at run time with:: 58 Or you can mount it at run time with::
59 59
60 mount -t tracefs nodev /sys/kernel/tracing 60 mount -t tracefs nodev /sys/kernel/tracing
61 61
62 For quicker access to that directory you may w 62 For quicker access to that directory you may want to make a soft link to
63 it:: 63 it::
64 64
65 ln -s /sys/kernel/tracing /tracing 65 ln -s /sys/kernel/tracing /tracing
66 66
67 .. attention:: 67 .. attention::
68 68
69 Before 4.1, all ftrace tracing control files 69 Before 4.1, all ftrace tracing control files were within the debugfs
70 file system, which is typically located at / 70 file system, which is typically located at /sys/kernel/debug/tracing.
71 For backward compatibility, when mounting th 71 For backward compatibility, when mounting the debugfs file system,
72 the tracefs file system will be automaticall 72 the tracefs file system will be automatically mounted at:
73 73
74 /sys/kernel/debug/tracing 74 /sys/kernel/debug/tracing
75 75
76 All files located in the tracefs file system 76 All files located in the tracefs file system will be located in that
77 debugfs file system directory as well. 77 debugfs file system directory as well.
78 78
79 .. attention:: 79 .. attention::
80 80
81 Any selected ftrace option will also create 81 Any selected ftrace option will also create the tracefs file system.
82 The rest of the document will assume that yo 82 The rest of the document will assume that you are in the ftrace directory
83 (cd /sys/kernel/tracing) and will only conce 83 (cd /sys/kernel/tracing) and will only concentrate on the files within that
84 directory and not distract from the content 84 directory and not distract from the content with the extended
85 "/sys/kernel/tracing" path name. 85 "/sys/kernel/tracing" path name.
86 86
87 That's it! (assuming that you have ftrace conf 87 That's it! (assuming that you have ftrace configured into your kernel)
88 88
89 After mounting tracefs you will have access to 89 After mounting tracefs you will have access to the control and output files
90 of ftrace. Here is a list of some of the key f 90 of ftrace. Here is a list of some of the key files:
91 91
92 92
93 Note: all time values are in microseconds. 93 Note: all time values are in microseconds.
94 94
95 current_tracer: 95 current_tracer:
96 96
97 This is used to set or display the cur 97 This is used to set or display the current tracer
98 that is configured. Changing the curre !! 98 that is configured.
99 the ring buffer content as well as the <<
100 99
101 available_tracers: 100 available_tracers:
102 101
103 This holds the different types of trac 102 This holds the different types of tracers that
104 have been compiled into the kernel. Th 103 have been compiled into the kernel. The
105 tracers listed here can be configured 104 tracers listed here can be configured by
106 echoing their name into current_tracer 105 echoing their name into current_tracer.
107 106
108 tracing_on: 107 tracing_on:
109 108
110 This sets or displays whether writing 109 This sets or displays whether writing to the trace
111 ring buffer is enabled. Echo 0 into th 110 ring buffer is enabled. Echo 0 into this file to disable
112 the tracer or 1 to enable it. Note, th 111 the tracer or 1 to enable it. Note, this only disables
113 writing to the ring buffer, the tracin 112 writing to the ring buffer, the tracing overhead may
114 still be occurring. 113 still be occurring.
115 114
116 The kernel function tracing_off() can 115 The kernel function tracing_off() can be used within the
117 kernel to disable writing to the ring 116 kernel to disable writing to the ring buffer, which will
118 set this file to "0". User space can r 117 set this file to "0". User space can re-enable tracing by
119 echoing "1" into the file. 118 echoing "1" into the file.
120 119
121 Note, the function and event trigger " 120 Note, the function and event trigger "traceoff" will also
122 set this file to zero and stop tracing 121 set this file to zero and stop tracing. Which can also
123 be re-enabled by user space using this 122 be re-enabled by user space using this file.
124 123
125 trace: 124 trace:
126 125
127 This file holds the output of the trac 126 This file holds the output of the trace in a human
128 readable format (described below). Ope !! 127 readable format (described below). Note, tracing is temporarily
129 writing with the O_TRUNC flag clears t !! 128 disabled while this file is being read (opened).
130 Note, this file is not a consumer. If <<
131 (no tracer running, or tracing_on is z <<
132 the same output each time it is read. <<
133 it may produce inconsistent results as <<
134 the entire buffer without consuming it <<
135 129
136 trace_pipe: 130 trace_pipe:
137 131
138 The output is the same as the "trace" 132 The output is the same as the "trace" file but this
139 file is meant to be streamed with live 133 file is meant to be streamed with live tracing.
140 Reads from this file will block until 134 Reads from this file will block until new data is
141 retrieved. Unlike the "trace" file, t 135 retrieved. Unlike the "trace" file, this file is a
142 consumer. This means reading from this 136 consumer. This means reading from this file causes
143 sequential reads to display more curre 137 sequential reads to display more current data. Once
144 data is read from this file, it is con 138 data is read from this file, it is consumed, and
145 will not be read again with a sequenti 139 will not be read again with a sequential read. The
146 "trace" file is static, and if the tra 140 "trace" file is static, and if the tracer is not
147 adding more data, it will display the 141 adding more data, it will display the same
148 information every time it is read. !! 142 information every time it is read. This file will not
>> 143 disable tracing while being read.
149 144
150 trace_options: 145 trace_options:
151 146
152 This file lets the user control the am 147 This file lets the user control the amount of data
153 that is displayed in one of the above 148 that is displayed in one of the above output
154 files. Options also exist to modify ho 149 files. Options also exist to modify how a tracer
155 or events work (stack traces, timestam 150 or events work (stack traces, timestamps, etc).
156 151
157 options: 152 options:
158 153
159 This is a directory that has a file fo 154 This is a directory that has a file for every available
160 trace option (also in trace_options). 155 trace option (also in trace_options). Options may also be set
161 or cleared by writing a "1" or "0" res 156 or cleared by writing a "1" or "0" respectively into the
162 corresponding file with the option nam 157 corresponding file with the option name.
163 158
164 tracing_max_latency: 159 tracing_max_latency:
165 160
166 Some of the tracers record the max lat 161 Some of the tracers record the max latency.
167 For example, the maximum time that int 162 For example, the maximum time that interrupts are disabled.
168 The maximum time is saved in this file 163 The maximum time is saved in this file. The max trace will also be
169 stored, and displayed by "trace". A ne 164 stored, and displayed by "trace". A new max trace will only be
170 recorded if the latency is greater tha 165 recorded if the latency is greater than the value in this file
171 (in microseconds). 166 (in microseconds).
172 167
173 By echoing in a time into this file, n 168 By echoing in a time into this file, no latency will be recorded
174 unless it is greater than the time in 169 unless it is greater than the time in this file.
175 170
176 tracing_thresh: 171 tracing_thresh:
177 172
178 Some latency tracers will record a tra 173 Some latency tracers will record a trace whenever the
179 latency is greater than the number in 174 latency is greater than the number in this file.
180 Only active when the file contains a n 175 Only active when the file contains a number greater than 0.
181 (in microseconds) 176 (in microseconds)
182 177
183 buffer_percent: <<
184 <<
185 This is the watermark for how much the <<
186 before a waiter is woken up. That is, <<
187 blocking read syscall on one of the pe <<
188 will block until the given amount of d <<
189 is in the ring buffer before it wakes <<
190 controls how the splice system calls a <<
191 <<
192 0 - means to wake up as soon as th <<
193 50 - means to wake up when roughly <<
194 are full. <<
195 100 - means to block until the ring <<
196 about to start overwriting the <<
197 <<
198 buffer_size_kb: 178 buffer_size_kb:
199 179
200 This sets or displays the number of ki 180 This sets or displays the number of kilobytes each CPU
201 buffer holds. By default, the trace bu 181 buffer holds. By default, the trace buffers are the same size
202 for each CPU. The displayed number is 182 for each CPU. The displayed number is the size of the
203 CPU buffer and not total size of all b 183 CPU buffer and not total size of all buffers. The
204 trace buffers are allocated in pages ( 184 trace buffers are allocated in pages (blocks of memory
205 that the kernel uses for allocation, u 185 that the kernel uses for allocation, usually 4 KB in size).
206 A few extra pages may be allocated to !! 186 If the last page allocated has room for more bytes
207 meta-data. If the last page allocated <<
208 than requested, the rest of the page w 187 than requested, the rest of the page will be used,
209 making the actual allocation bigger th 188 making the actual allocation bigger than requested or shown.
210 ( Note, the size may not be a multiple 189 ( Note, the size may not be a multiple of the page size
211 due to buffer management meta-data. ) 190 due to buffer management meta-data. )
212 191
213 Buffer sizes for individual CPUs may v 192 Buffer sizes for individual CPUs may vary
214 (see "per_cpu/cpu0/buffer_size_kb" bel 193 (see "per_cpu/cpu0/buffer_size_kb" below), and if they do
215 this file will show "X". 194 this file will show "X".
216 195
217 buffer_total_size_kb: 196 buffer_total_size_kb:
218 197
219 This displays the total combined size 198 This displays the total combined size of all the trace buffers.
220 199
221 buffer_subbuf_size_kb: <<
222 <<
223 This sets or displays the sub buffer s <<
224 into several same size "sub buffers". <<
225 the size of the sub buffer. Normally, <<
226 architecture's page (4K on x86). The s <<
227 at the start which also limits the siz <<
228 the sub buffer is a page size, no even <<
229 size minus the sub buffer meta data. <<
230 <<
231 Note, the buffer_subbuf_size_kb is a w <<
232 minimum size of the subbuffer. The ker <<
233 implementation details, or simply fail <<
234 not handle the request. <<
235 <<
236 Changing the sub buffer size allows fo <<
237 page size. <<
238 <<
239 Note: When changing the sub-buffer siz <<
240 data in the ring buffer and the snapsh <<
241 <<
242 free_buffer: 200 free_buffer:
243 201
244 If a process is performing tracing, an 202 If a process is performing tracing, and the ring buffer should be
245 shrunk "freed" when the process is fin 203 shrunk "freed" when the process is finished, even if it were to be
246 killed by a signal, this file can be u 204 killed by a signal, this file can be used for that purpose. On close
247 of this file, the ring buffer will be 205 of this file, the ring buffer will be resized to its minimum size.
248 Having a process that is tracing also 206 Having a process that is tracing also open this file, when the process
249 exits its file descriptor for this fil 207 exits its file descriptor for this file will be closed, and in doing so,
250 the ring buffer will be "freed". 208 the ring buffer will be "freed".
251 209
252 It may also stop tracing if disable_on 210 It may also stop tracing if disable_on_free option is set.
253 211
254 tracing_cpumask: 212 tracing_cpumask:
255 213
256 This is a mask that lets the user only 214 This is a mask that lets the user only trace on specified CPUs.
257 The format is a hex string representin 215 The format is a hex string representing the CPUs.
258 216
259 set_ftrace_filter: 217 set_ftrace_filter:
260 218
261 When dynamic ftrace is configured in ( 219 When dynamic ftrace is configured in (see the
262 section below "dynamic ftrace"), the c 220 section below "dynamic ftrace"), the code is dynamically
263 modified (code text rewrite) to disabl 221 modified (code text rewrite) to disable calling of the
264 function profiler (mcount). This lets 222 function profiler (mcount). This lets tracing be configured
265 in with practically no overhead in per 223 in with practically no overhead in performance. This also
266 has a side effect of enabling or disab 224 has a side effect of enabling or disabling specific functions
267 to be traced. Echoing names of functio 225 to be traced. Echoing names of functions into this file
268 will limit the trace to only those fun 226 will limit the trace to only those functions.
269 This influences the tracers "function" 227 This influences the tracers "function" and "function_graph"
270 and thus also function profiling (see 228 and thus also function profiling (see "function_profile_enabled").
271 229
272 The functions listed in "available_fil 230 The functions listed in "available_filter_functions" are what
273 can be written into this file. 231 can be written into this file.
274 232
275 This interface also allows for command 233 This interface also allows for commands to be used. See the
276 "Filter commands" section for more det 234 "Filter commands" section for more details.
277 235
278 As a speed up, since processing string !! 236 As a speed up, since processing strings can't be quite expensive
279 and requires a check of all functions 237 and requires a check of all functions registered to tracing, instead
280 an index can be written into this file 238 an index can be written into this file. A number (starting with "1")
281 written will instead select the same c 239 written will instead select the same corresponding at the line position
282 of the "available_filter_functions" fi 240 of the "available_filter_functions" file.
283 241
284 set_ftrace_notrace: 242 set_ftrace_notrace:
285 243
286 This has an effect opposite to that of 244 This has an effect opposite to that of
287 set_ftrace_filter. Any function that i 245 set_ftrace_filter. Any function that is added here will not
288 be traced. If a function exists in bot 246 be traced. If a function exists in both set_ftrace_filter
289 and set_ftrace_notrace, the function w 247 and set_ftrace_notrace, the function will _not_ be traced.
290 248
291 set_ftrace_pid: 249 set_ftrace_pid:
292 250
293 Have the function tracer only trace th 251 Have the function tracer only trace the threads whose PID are
294 listed in this file. 252 listed in this file.
295 253
296 If the "function-fork" option is set, 254 If the "function-fork" option is set, then when a task whose
297 PID is listed in this file forks, the 255 PID is listed in this file forks, the child's PID will
298 automatically be added to this file, a 256 automatically be added to this file, and the child will be
299 traced by the function tracer as well. 257 traced by the function tracer as well. This option will also
300 cause PIDs of tasks that exit to be re 258 cause PIDs of tasks that exit to be removed from the file.
301 259
302 set_ftrace_notrace_pid: <<
303 <<
304 Have the function tracer ignore thread <<
305 this file. <<
306 <<
307 If the "function-fork" option is set, <<
308 PID is listed in this file forks, the <<
309 automatically be added to this file, a <<
310 traced by the function tracer as well. <<
311 cause PIDs of tasks that exit to be re <<
312 <<
313 If a PID is in both this file and "set <<
314 file takes precedence, and the thread <<
315 <<
316 set_event_pid: 260 set_event_pid:
317 261
318 Have the events only trace a task with 262 Have the events only trace a task with a PID listed in this file.
319 Note, sched_switch and sched_wake_up w 263 Note, sched_switch and sched_wake_up will also trace events
320 listed in this file. 264 listed in this file.
321 265
322 To have the PIDs of children of tasks 266 To have the PIDs of children of tasks with their PID in this file
323 added on fork, enable the "event-fork" 267 added on fork, enable the "event-fork" option. That option will also
324 cause the PIDs of tasks to be removed 268 cause the PIDs of tasks to be removed from this file when the task
325 exits. 269 exits.
326 270
327 set_event_notrace_pid: <<
328 <<
329 Have the events not trace a task with <<
330 Note, sched_switch and sched_wakeup wi <<
331 in this file, even if a thread's PID i <<
332 sched_switch or sched_wakeup events al <<
333 be traced. <<
334 <<
335 To have the PIDs of children of tasks <<
336 added on fork, enable the "event-fork" <<
337 cause the PIDs of tasks to be removed <<
338 exits. <<
339 <<
340 set_graph_function: 271 set_graph_function:
341 272
342 Functions listed in this file will cau 273 Functions listed in this file will cause the function graph
343 tracer to only trace these functions a 274 tracer to only trace these functions and the functions that
344 they call. (See the section "dynamic f 275 they call. (See the section "dynamic ftrace" for more details).
345 Note, set_ftrace_filter and set_ftrace 276 Note, set_ftrace_filter and set_ftrace_notrace still affects
346 what functions are being traced. 277 what functions are being traced.
347 278
348 set_graph_notrace: 279 set_graph_notrace:
349 280
350 Similar to set_graph_function, but wil 281 Similar to set_graph_function, but will disable function graph
351 tracing when the function is hit until 282 tracing when the function is hit until it exits the function.
352 This makes it possible to ignore traci 283 This makes it possible to ignore tracing functions that are called
353 by a specific function. 284 by a specific function.
354 285
355 available_filter_functions: 286 available_filter_functions:
356 287
357 This lists the functions that ftrace h 288 This lists the functions that ftrace has processed and can trace.
358 These are the function names that you 289 These are the function names that you can pass to
359 "set_ftrace_filter", "set_ftrace_notra 290 "set_ftrace_filter", "set_ftrace_notrace",
360 "set_graph_function", or "set_graph_no 291 "set_graph_function", or "set_graph_notrace".
361 (See the section "dynamic ftrace" belo 292 (See the section "dynamic ftrace" below for more details.)
362 293
363 available_filter_functions_addrs: <<
364 <<
365 Similar to available_filter_functions, <<
366 for each function. The displayed addre <<
367 and can differ from /proc/kallsyms add <<
368 <<
369 dyn_ftrace_total_info: 294 dyn_ftrace_total_info:
370 295
371 This file is for debugging purposes. T 296 This file is for debugging purposes. The number of functions that
372 have been converted to nops and are av 297 have been converted to nops and are available to be traced.
373 298
374 enabled_functions: 299 enabled_functions:
375 300
376 This file is more for debugging ftrace 301 This file is more for debugging ftrace, but can also be useful
377 in seeing if any function has a callba 302 in seeing if any function has a callback attached to it.
378 Not only does the trace infrastructure 303 Not only does the trace infrastructure use ftrace function
379 trace utility, but other subsystems mi 304 trace utility, but other subsystems might too. This file
380 displays all functions that have a cal 305 displays all functions that have a callback attached to them
381 as well as the number of callbacks tha 306 as well as the number of callbacks that have been attached.
382 Note, a callback may also call multipl 307 Note, a callback may also call multiple functions which will
383 not be listed in this count. 308 not be listed in this count.
384 309
385 If the callback registered to be trace 310 If the callback registered to be traced by a function with
386 the "save regs" attribute (thus even m 311 the "save regs" attribute (thus even more overhead), a 'R'
387 will be displayed on the same line as 312 will be displayed on the same line as the function that
388 is returning registers. 313 is returning registers.
389 314
390 If the callback registered to be trace 315 If the callback registered to be traced by a function with
391 the "ip modify" attribute (thus the re 316 the "ip modify" attribute (thus the regs->ip can be changed),
392 an 'I' will be displayed on the same l 317 an 'I' will be displayed on the same line as the function that
393 can be overridden. 318 can be overridden.
394 319
395 If a non ftrace trampoline is attached <<
396 Note, normal ftrace trampolines can al <<
397 "direct" trampoline can be attached to <<
398 <<
399 Some architectures can not call direct <<
400 the ftrace ops function located above <<
401 such cases an 'O' will be displayed. <<
402 <<
403 If a function had either the "ip modif <<
404 it in the past, a 'M' will be shown. T <<
405 used to know if a function was every m <<
406 and can be used for debugging. <<
407 <<
408 If the architecture supports it, it wi 320 If the architecture supports it, it will also show what callback
409 is being directly called by the functi 321 is being directly called by the function. If the count is greater
410 than 1 it most likely will be ftrace_o 322 than 1 it most likely will be ftrace_ops_list_func().
411 323
412 If the callback of a function jumps to !! 324 If the callback of the function jumps to a trampoline that is
413 specific to the callback and which is !! 325 specific to a the callback and not the standard trampoline,
414 its address will be printed as well as 326 its address will be printed as well as the function that the
415 trampoline calls. 327 trampoline calls.
416 328
417 touched_functions: <<
418 <<
419 This file contains all the functions t <<
420 to it via the ftrace infrastructure. I <<
421 enabled_functions but shows all functi <<
422 traced. <<
423 <<
424 To see any function that has every bee <<
425 direct trampoline, one can perform the <<
426 <<
427 grep ' M ' /sys/kernel/tracing/touched <<
428 <<
429 function_profile_enabled: 329 function_profile_enabled:
430 330
431 When set it will enable all functions 331 When set it will enable all functions with either the function
432 tracer, or if configured, the function 332 tracer, or if configured, the function graph tracer. It will
433 keep a histogram of the number of func 333 keep a histogram of the number of functions that were called
434 and if the function graph tracer was c 334 and if the function graph tracer was configured, it will also keep
435 track of the time spent in those funct 335 track of the time spent in those functions. The histogram
436 content can be displayed in the files: 336 content can be displayed in the files:
437 337
438 trace_stat/function<cpu> ( function0, 338 trace_stat/function<cpu> ( function0, function1, etc).
439 339
440 trace_stat: 340 trace_stat:
441 341
442 A directory that holds different traci 342 A directory that holds different tracing stats.
443 343
444 kprobe_events: 344 kprobe_events:
445 345
446 Enable dynamic trace points. See kprob !! 346 Enable dynamic trace points. See kprobetrace.txt.
447 347
448 kprobe_profile: 348 kprobe_profile:
449 349
450 Dynamic trace points stats. See kprobe !! 350 Dynamic trace points stats. See kprobetrace.txt.
451 351
452 max_graph_depth: 352 max_graph_depth:
453 353
454 Used with the function graph tracer. T 354 Used with the function graph tracer. This is the max depth
455 it will trace into a function. Setting 355 it will trace into a function. Setting this to a value of
456 one will show only the first kernel fu 356 one will show only the first kernel function that is called
457 from user space. 357 from user space.
458 358
459 printk_formats: 359 printk_formats:
460 360
461 This is for tools that read the raw fo 361 This is for tools that read the raw format files. If an event in
462 the ring buffer references a string, o 362 the ring buffer references a string, only a pointer to the string
463 is recorded into the buffer and not th 363 is recorded into the buffer and not the string itself. This prevents
464 tools from knowing what that string wa 364 tools from knowing what that string was. This file displays the string
465 and address for the string allowing to 365 and address for the string allowing tools to map the pointers to what
466 the strings were. 366 the strings were.
467 367
468 saved_cmdlines: 368 saved_cmdlines:
469 369
470 Only the pid of the task is recorded i 370 Only the pid of the task is recorded in a trace event unless
471 the event specifically saves the task 371 the event specifically saves the task comm as well. Ftrace
472 makes a cache of pid mappings to comms 372 makes a cache of pid mappings to comms to try to display
473 comms for events. If a pid for a comm 373 comms for events. If a pid for a comm is not listed, then
474 "<...>" is displayed in the output. 374 "<...>" is displayed in the output.
475 375
476 If the option "record-cmd" is set to " 376 If the option "record-cmd" is set to "0", then comms of tasks
477 will not be saved during recording. By 377 will not be saved during recording. By default, it is enabled.
478 378
479 saved_cmdlines_size: 379 saved_cmdlines_size:
480 380
481 By default, 128 comms are saved (see " 381 By default, 128 comms are saved (see "saved_cmdlines" above). To
482 increase or decrease the amount of com 382 increase or decrease the amount of comms that are cached, echo
483 the number of comms to cache into this !! 383 in a the number of comms to cache, into this file.
484 384
485 saved_tgids: 385 saved_tgids:
486 386
487 If the option "record-tgid" is set, on 387 If the option "record-tgid" is set, on each scheduling context switch
488 the Task Group ID of a task is saved i 388 the Task Group ID of a task is saved in a table mapping the PID of
489 the thread to its TGID. By default, th 389 the thread to its TGID. By default, the "record-tgid" option is
490 disabled. 390 disabled.
491 391
492 snapshot: 392 snapshot:
493 393
494 This displays the "snapshot" buffer an 394 This displays the "snapshot" buffer and also lets the user
495 take a snapshot of the current running 395 take a snapshot of the current running trace.
496 See the "Snapshot" section below for m 396 See the "Snapshot" section below for more details.
497 397
498 stack_max_size: 398 stack_max_size:
499 399
500 When the stack tracer is activated, th 400 When the stack tracer is activated, this will display the
501 maximum stack size it has encountered. 401 maximum stack size it has encountered.
502 See the "Stack Trace" section below. 402 See the "Stack Trace" section below.
503 403
504 stack_trace: 404 stack_trace:
505 405
506 This displays the stack back trace of 406 This displays the stack back trace of the largest stack
507 that was encountered when the stack tr 407 that was encountered when the stack tracer is activated.
508 See the "Stack Trace" section below. 408 See the "Stack Trace" section below.
509 409
510 stack_trace_filter: 410 stack_trace_filter:
511 411
512 This is similar to "set_ftrace_filter" 412 This is similar to "set_ftrace_filter" but it limits what
513 functions the stack tracer will check. 413 functions the stack tracer will check.
514 414
515 trace_clock: 415 trace_clock:
516 416
517 Whenever an event is recorded into the 417 Whenever an event is recorded into the ring buffer, a
518 "timestamp" is added. This stamp comes 418 "timestamp" is added. This stamp comes from a specified
519 clock. By default, ftrace uses the "lo 419 clock. By default, ftrace uses the "local" clock. This
520 clock is very fast and strictly per cp 420 clock is very fast and strictly per cpu, but on some
521 systems it may not be monotonic with r 421 systems it may not be monotonic with respect to other
522 CPUs. In other words, the local clocks 422 CPUs. In other words, the local clocks may not be in sync
523 with local clocks on other CPUs. 423 with local clocks on other CPUs.
524 424
525 Usual clocks for tracing:: 425 Usual clocks for tracing::
526 426
527 # cat trace_clock 427 # cat trace_clock
528 [local] global counter x86-tsc 428 [local] global counter x86-tsc
529 429
530 The clock with the square brackets aro 430 The clock with the square brackets around it is the one in effect.
531 431
532 local: 432 local:
533 Default clock, but may not be 433 Default clock, but may not be in sync across CPUs
534 434
535 global: 435 global:
536 This clock is in sync with all 436 This clock is in sync with all CPUs but may
537 be a bit slower than the local 437 be a bit slower than the local clock.
538 438
539 counter: 439 counter:
540 This is not a clock at all, bu 440 This is not a clock at all, but literally an atomic
541 counter. It counts up one by o 441 counter. It counts up one by one, but is in sync
542 with all CPUs. This is useful 442 with all CPUs. This is useful when you need to
543 know exactly the order events 443 know exactly the order events occurred with respect to
544 each other on different CPUs. 444 each other on different CPUs.
545 445
546 uptime: 446 uptime:
547 This uses the jiffies counter 447 This uses the jiffies counter and the time stamp
548 is relative to the time since 448 is relative to the time since boot up.
549 449
550 perf: 450 perf:
551 This makes ftrace use the same 451 This makes ftrace use the same clock that perf uses.
552 Eventually perf will be able t 452 Eventually perf will be able to read ftrace buffers
553 and this will help out in inte 453 and this will help out in interleaving the data.
554 454
555 x86-tsc: 455 x86-tsc:
556 Architectures may define their 456 Architectures may define their own clocks. For
557 example, x86 uses its own TSC 457 example, x86 uses its own TSC cycle clock here.
558 458
559 ppc-tb: 459 ppc-tb:
560 This uses the powerpc timebase 460 This uses the powerpc timebase register value.
561 This is in sync across CPUs an 461 This is in sync across CPUs and can also be used
562 to correlate events across hyp 462 to correlate events across hypervisor/guest if
563 tb_offset is known. 463 tb_offset is known.
564 464
565 mono: 465 mono:
566 This uses the fast monotonic c 466 This uses the fast monotonic clock (CLOCK_MONOTONIC)
567 which is monotonic and is subj 467 which is monotonic and is subject to NTP rate adjustments.
568 468
569 mono_raw: 469 mono_raw:
570 This is the raw monotonic cloc 470 This is the raw monotonic clock (CLOCK_MONOTONIC_RAW)
571 which is monotonic but is not 471 which is monotonic but is not subject to any rate adjustments
572 and ticks at the same rate as 472 and ticks at the same rate as the hardware clocksource.
573 473
574 boot: 474 boot:
575 This is the boot clock (CLOCK_ 475 This is the boot clock (CLOCK_BOOTTIME) and is based on the
576 fast monotonic clock, but also 476 fast monotonic clock, but also accounts for time spent in
577 suspend. Since the clock acces 477 suspend. Since the clock access is designed for use in
578 tracing in the suspend path, s 478 tracing in the suspend path, some side effects are possible
579 if clock is accessed after the 479 if clock is accessed after the suspend time is accounted before
580 the fast mono clock is updated 480 the fast mono clock is updated. In this case, the clock update
581 appears to happen slightly soo 481 appears to happen slightly sooner than it normally would have.
582 Also on 32-bit systems, it's p 482 Also on 32-bit systems, it's possible that the 64-bit boot offset
583 sees a partial update. These e 483 sees a partial update. These effects are rare and post
584 processing should be able to h 484 processing should be able to handle them. See comments in the
585 ktime_get_boot_fast_ns() funct 485 ktime_get_boot_fast_ns() function for more information.
586 486
587 tai: <<
588 This is the tai clock (CLOCK_T <<
589 clock time. However, this cloc <<
590 discontinuities and backwards <<
591 seconds. Since the clock acces <<
592 side effects are possible. The <<
593 readouts in case the internal <<
594 by setting the system time or <<
595 These effects are rare and pos <<
596 handle them. See comments in t <<
597 function for more information. <<
598 <<
599 To set a clock, simply echo the clock 487 To set a clock, simply echo the clock name into this file::
600 488
601 # echo global > trace_clock 489 # echo global > trace_clock
602 490
603 Setting a clock clears the ring buffer <<
604 "snapshot" buffer. <<
605 <<
606 trace_marker: 491 trace_marker:
607 492
608 This is a very useful file for synchro 493 This is a very useful file for synchronizing user space
609 with events happening in the kernel. W 494 with events happening in the kernel. Writing strings into
610 this file will be written into the ftr 495 this file will be written into the ftrace buffer.
611 496
612 It is useful in applications to open t 497 It is useful in applications to open this file at the start
613 of the application and just reference 498 of the application and just reference the file descriptor
614 for the file:: 499 for the file::
615 500
616 void trace_write(const char *f 501 void trace_write(const char *fmt, ...)
617 { 502 {
618 va_list ap; 503 va_list ap;
619 char buf[256]; 504 char buf[256];
620 int n; 505 int n;
621 506
622 if (trace_fd < 0) 507 if (trace_fd < 0)
623 return; 508 return;
624 509
625 va_start(ap, fmt); 510 va_start(ap, fmt);
626 n = vsnprintf(buf, 256 511 n = vsnprintf(buf, 256, fmt, ap);
627 va_end(ap); 512 va_end(ap);
628 513
629 write(trace_fd, buf, n 514 write(trace_fd, buf, n);
630 } 515 }
631 516
632 start:: 517 start::
633 518
634 trace_fd = open("trace_marker" !! 519 trace_fd = open("trace_marker", WR_ONLY);
635 520
636 Note: Writing into the trace_marker fi 521 Note: Writing into the trace_marker file can also initiate triggers
637 that are written into /sys/kerne 522 that are written into /sys/kernel/tracing/events/ftrace/print/trigger
638 See "Event triggers" in Document 523 See "Event triggers" in Documentation/trace/events.rst and an
639 example in Documentation/trace/h 524 example in Documentation/trace/histogram.rst (Section 3.)
640 525
641 trace_marker_raw: 526 trace_marker_raw:
642 527
643 This is similar to trace_marker above, !! 528 This is similar to trace_marker above, but is meant for for binary data
644 to be written to it, where a tool can 529 to be written to it, where a tool can be used to parse the data
645 from trace_pipe_raw. 530 from trace_pipe_raw.
646 531
647 uprobe_events: 532 uprobe_events:
648 533
649 Add dynamic tracepoints in programs. 534 Add dynamic tracepoints in programs.
650 See uprobetracer.rst !! 535 See uprobetracer.txt
651 536
652 uprobe_profile: 537 uprobe_profile:
653 538
654 Uprobe statistics. See uprobetrace.txt 539 Uprobe statistics. See uprobetrace.txt
655 540
656 instances: 541 instances:
657 542
658 This is a way to make multiple trace b 543 This is a way to make multiple trace buffers where different
659 events can be recorded in different bu 544 events can be recorded in different buffers.
660 See "Instances" section below. 545 See "Instances" section below.
661 546
662 events: 547 events:
663 548
664 This is the trace event directory. It 549 This is the trace event directory. It holds event tracepoints
665 (also known as static tracepoints) tha 550 (also known as static tracepoints) that have been compiled
666 into the kernel. It shows what event t 551 into the kernel. It shows what event tracepoints exist
667 and how they are grouped by system. Th 552 and how they are grouped by system. There are "enable"
668 files at various levels that can enabl 553 files at various levels that can enable the tracepoints
669 when a "1" is written to them. 554 when a "1" is written to them.
670 555
671 See events.rst for more information. !! 556 See events.txt for more information.
672 557
673 set_event: 558 set_event:
674 559
675 By echoing in the event into this file 560 By echoing in the event into this file, will enable that event.
676 561
677 See events.rst for more information. !! 562 See events.txt for more information.
678 563
679 available_events: 564 available_events:
680 565
681 A list of events that can be enabled i 566 A list of events that can be enabled in tracing.
682 567
683 See events.rst for more information. !! 568 See events.txt for more information.
684 569
685 timestamp_mode: 570 timestamp_mode:
686 571
687 Certain tracers may change the timesta 572 Certain tracers may change the timestamp mode used when
688 logging trace events into the event bu 573 logging trace events into the event buffer. Events with
689 different modes can coexist within a b 574 different modes can coexist within a buffer but the mode in
690 effect when an event is logged determi 575 effect when an event is logged determines which timestamp mode
691 is used for that event. The default t 576 is used for that event. The default timestamp mode is
692 'delta'. 577 'delta'.
693 578
694 Usual timestamp modes for tracing: 579 Usual timestamp modes for tracing:
695 580
696 # cat timestamp_mode 581 # cat timestamp_mode
697 [delta] absolute 582 [delta] absolute
698 583
699 The timestamp mode with the square b 584 The timestamp mode with the square brackets around it is the
700 one in effect. 585 one in effect.
701 586
702 delta: Default timestamp mode - time 587 delta: Default timestamp mode - timestamp is a delta against
703 a per-buffer timestamp. 588 a per-buffer timestamp.
704 589
705 absolute: The timestamp is a full ti 590 absolute: The timestamp is a full timestamp, not a delta
706 against some other value. As 591 against some other value. As such it takes up more
707 space and is less efficient. 592 space and is less efficient.
708 593
709 hwlat_detector: 594 hwlat_detector:
710 595
711 Directory for the Hardware Latency Det 596 Directory for the Hardware Latency Detector.
712 See "Hardware Latency Detector" sectio 597 See "Hardware Latency Detector" section below.
713 598
714 per_cpu: 599 per_cpu:
715 600
716 This is a directory that contains the 601 This is a directory that contains the trace per_cpu information.
717 602
718 per_cpu/cpu0/buffer_size_kb: 603 per_cpu/cpu0/buffer_size_kb:
719 604
720 The ftrace buffer is defined per_cpu. 605 The ftrace buffer is defined per_cpu. That is, there's a separate
721 buffer for each CPU to allow writes to 606 buffer for each CPU to allow writes to be done atomically,
722 and free from cache bouncing. These bu 607 and free from cache bouncing. These buffers may have different
723 size buffers. This file is similar to 608 size buffers. This file is similar to the buffer_size_kb
724 file, but it only displays or sets the 609 file, but it only displays or sets the buffer size for the
725 specific CPU. (here cpu0). 610 specific CPU. (here cpu0).
726 611
727 per_cpu/cpu0/trace: 612 per_cpu/cpu0/trace:
728 613
729 This is similar to the "trace" file, b 614 This is similar to the "trace" file, but it will only display
730 the data specific for the CPU. If writ 615 the data specific for the CPU. If written to, it only clears
731 the specific CPU buffer. 616 the specific CPU buffer.
732 617
733 per_cpu/cpu0/trace_pipe 618 per_cpu/cpu0/trace_pipe
734 619
735 This is similar to the "trace_pipe" fi 620 This is similar to the "trace_pipe" file, and is a consuming
736 read, but it will only display (and co 621 read, but it will only display (and consume) the data specific
737 for the CPU. 622 for the CPU.
738 623
739 per_cpu/cpu0/trace_pipe_raw 624 per_cpu/cpu0/trace_pipe_raw
740 625
741 For tools that can parse the ftrace ri 626 For tools that can parse the ftrace ring buffer binary format,
742 the trace_pipe_raw file can be used to 627 the trace_pipe_raw file can be used to extract the data
743 from the ring buffer directly. With th 628 from the ring buffer directly. With the use of the splice()
744 system call, the buffer data can be qu 629 system call, the buffer data can be quickly transferred to
745 a file or to the network where a serve 630 a file or to the network where a server is collecting the
746 data. 631 data.
747 632
748 Like trace_pipe, this is a consuming r 633 Like trace_pipe, this is a consuming reader, where multiple
749 reads will always produce different da 634 reads will always produce different data.
750 635
751 per_cpu/cpu0/snapshot: 636 per_cpu/cpu0/snapshot:
752 637
753 This is similar to the main "snapshot" 638 This is similar to the main "snapshot" file, but will only
754 snapshot the current CPU (if supported 639 snapshot the current CPU (if supported). It only displays
755 the content of the snapshot for a give 640 the content of the snapshot for a given CPU, and if
756 written to, only clears this CPU buffe 641 written to, only clears this CPU buffer.
757 642
758 per_cpu/cpu0/snapshot_raw: 643 per_cpu/cpu0/snapshot_raw:
759 644
760 Similar to the trace_pipe_raw, but wil 645 Similar to the trace_pipe_raw, but will read the binary format
761 from the snapshot buffer for the given 646 from the snapshot buffer for the given CPU.
762 647
763 per_cpu/cpu0/stats: 648 per_cpu/cpu0/stats:
764 649
765 This displays certain stats about the 650 This displays certain stats about the ring buffer:
766 651
767 entries: 652 entries:
768 The number of events that are 653 The number of events that are still in the buffer.
769 654
770 overrun: 655 overrun:
771 The number of lost events due 656 The number of lost events due to overwriting when
772 the buffer was full. 657 the buffer was full.
773 658
774 commit overrun: 659 commit overrun:
775 Should always be zero. 660 Should always be zero.
776 This gets set if so many event 661 This gets set if so many events happened within a nested
777 event (ring buffer is re-entra 662 event (ring buffer is re-entrant), that it fills the
778 buffer and starts dropping eve 663 buffer and starts dropping events.
779 664
780 bytes: 665 bytes:
781 Bytes actually read (not overw 666 Bytes actually read (not overwritten).
782 667
783 oldest event ts: 668 oldest event ts:
784 The oldest timestamp in the bu 669 The oldest timestamp in the buffer
785 670
786 now ts: 671 now ts:
787 The current timestamp 672 The current timestamp
788 673
789 dropped events: 674 dropped events:
790 Events lost due to overwrite o 675 Events lost due to overwrite option being off.
791 676
792 read events: 677 read events:
793 The number of events read. 678 The number of events read.
794 679
795 The Tracers 680 The Tracers
796 ----------- 681 -----------
797 682
798 Here is the list of current tracers that may b 683 Here is the list of current tracers that may be configured.
799 684
800 "function" 685 "function"
801 686
802 Function call tracer to trace all kern 687 Function call tracer to trace all kernel functions.
803 688
804 "function_graph" 689 "function_graph"
805 690
806 Similar to the function tracer except 691 Similar to the function tracer except that the
807 function tracer probes the functions o 692 function tracer probes the functions on their entry
808 whereas the function graph tracer trac 693 whereas the function graph tracer traces on both entry
809 and exit of the functions. It then pro 694 and exit of the functions. It then provides the ability
810 to draw a graph of function calls simi 695 to draw a graph of function calls similar to C code
811 source. 696 source.
812 697
813 "blk" 698 "blk"
814 699
815 The block tracer. The tracer used by t 700 The block tracer. The tracer used by the blktrace user
816 application. 701 application.
817 702
818 "hwlat" 703 "hwlat"
819 704
820 The Hardware Latency tracer is used to 705 The Hardware Latency tracer is used to detect if the hardware
821 produces any latency. See "Hardware La 706 produces any latency. See "Hardware Latency Detector" section
822 below. 707 below.
823 708
824 "irqsoff" 709 "irqsoff"
825 710
826 Traces the areas that disable interrup 711 Traces the areas that disable interrupts and saves
827 the trace with the longest max latency 712 the trace with the longest max latency.
828 See tracing_max_latency. When a new ma 713 See tracing_max_latency. When a new max is recorded,
829 it replaces the old trace. It is best 714 it replaces the old trace. It is best to view this
830 trace with the latency-format option e 715 trace with the latency-format option enabled, which
831 happens automatically when the tracer 716 happens automatically when the tracer is selected.
832 717
833 "preemptoff" 718 "preemptoff"
834 719
835 Similar to irqsoff but traces and reco 720 Similar to irqsoff but traces and records the amount of
836 time for which preemption is disabled. 721 time for which preemption is disabled.
837 722
838 "preemptirqsoff" 723 "preemptirqsoff"
839 724
840 Similar to irqsoff and preemptoff, but 725 Similar to irqsoff and preemptoff, but traces and
841 records the largest time for which irq 726 records the largest time for which irqs and/or preemption
842 is disabled. 727 is disabled.
843 728
844 "wakeup" 729 "wakeup"
845 730
846 Traces and records the max latency tha 731 Traces and records the max latency that it takes for
847 the highest priority task to get sched 732 the highest priority task to get scheduled after
848 it has been woken up. 733 it has been woken up.
849 Traces all tasks as an average develop 734 Traces all tasks as an average developer would expect.
850 735
851 "wakeup_rt" 736 "wakeup_rt"
852 737
853 Traces and records the max latency tha 738 Traces and records the max latency that it takes for just
854 RT tasks (as the current "wakeup" does 739 RT tasks (as the current "wakeup" does). This is useful
855 for those interested in wake up timing 740 for those interested in wake up timings of RT tasks.
856 741
857 "wakeup_dl" 742 "wakeup_dl"
858 743
859 Traces and records the max latency tha 744 Traces and records the max latency that it takes for
860 a SCHED_DEADLINE task to be woken (as 745 a SCHED_DEADLINE task to be woken (as the "wakeup" and
861 "wakeup_rt" does). 746 "wakeup_rt" does).
862 747
863 "mmiotrace" 748 "mmiotrace"
864 749
865 A special tracer that is used to trace 750 A special tracer that is used to trace binary module.
866 It will trace all the calls that a mod 751 It will trace all the calls that a module makes to the
867 hardware. Everything it writes and rea 752 hardware. Everything it writes and reads from the I/O
868 as well. 753 as well.
869 754
870 "branch" 755 "branch"
871 756
872 This tracer can be configured when tra 757 This tracer can be configured when tracing likely/unlikely
873 calls within the kernel. It will trace 758 calls within the kernel. It will trace when a likely and
874 unlikely branch is hit and if it was c 759 unlikely branch is hit and if it was correct in its prediction
875 of being correct. 760 of being correct.
876 761
877 "nop" 762 "nop"
878 763
879 This is the "trace nothing" tracer. To 764 This is the "trace nothing" tracer. To remove all
880 tracers from tracing simply echo "nop" 765 tracers from tracing simply echo "nop" into
881 current_tracer. 766 current_tracer.
882 767
883 Error conditions 768 Error conditions
884 ---------------- 769 ----------------
885 770
886 For most ftrace commands, failure modes are 771 For most ftrace commands, failure modes are obvious and communicated
887 using standard return codes. 772 using standard return codes.
888 773
889 For other more involved commands, extended e 774 For other more involved commands, extended error information may be
890 available via the tracing/error_log file. F 775 available via the tracing/error_log file. For the commands that
891 support it, reading the tracing/error_log fi 776 support it, reading the tracing/error_log file after an error will
892 display more detailed information about what 777 display more detailed information about what went wrong, if
893 information is available. The tracing/error 778 information is available. The tracing/error_log file is a circular
894 error log displaying a small number (current 779 error log displaying a small number (currently, 8) of ftrace errors
895 for the last (8) failed commands. 780 for the last (8) failed commands.
896 781
897 The extended error information and usage tak 782 The extended error information and usage takes the form shown in
898 this example:: 783 this example::
899 784
900 # echo xxx > /sys/kernel/tracing/events/sc !! 785 # echo xxx > /sys/kernel/debug/tracing/events/sched/sched_wakeup/trigger
901 echo: write error: Invalid argument 786 echo: write error: Invalid argument
902 787
903 # cat /sys/kernel/tracing/error_log !! 788 # cat /sys/kernel/debug/tracing/error_log
904 [ 5348.887237] location: error: Couldn't y 789 [ 5348.887237] location: error: Couldn't yyy: zzz
905 Command: xxx 790 Command: xxx
906 ^ 791 ^
907 [ 7517.023364] location: error: Bad rrr: s 792 [ 7517.023364] location: error: Bad rrr: sss
908 Command: ppp qqq 793 Command: ppp qqq
909 ^ 794 ^
910 795
911 To clear the error log, echo the empty strin 796 To clear the error log, echo the empty string into it::
912 797
913 # echo > /sys/kernel/tracing/error_log !! 798 # echo > /sys/kernel/debug/tracing/error_log
914 799
915 Examples of using the tracer 800 Examples of using the tracer
916 ---------------------------- 801 ----------------------------
917 802
918 Here are typical examples of using the tracers 803 Here are typical examples of using the tracers when controlling
919 them only with the tracefs interface (without 804 them only with the tracefs interface (without using any
920 user-land utilities). 805 user-land utilities).
921 806
922 Output format: 807 Output format:
923 -------------- 808 --------------
924 809
925 Here is an example of the output format of the 810 Here is an example of the output format of the file "trace"::
926 811
927 # tracer: function 812 # tracer: function
928 # 813 #
929 # entries-in-buffer/entries-written: 140080/ 814 # entries-in-buffer/entries-written: 140080/250280 #P:4
930 # 815 #
931 # _-----=> irqs 816 # _-----=> irqs-off
932 # / _----=> need 817 # / _----=> need-resched
933 # | / _---=> hard 818 # | / _---=> hardirq/softirq
934 # || / _--=> pree 819 # || / _--=> preempt-depth
935 # ||| / delay 820 # ||| / delay
936 # TASK-PID CPU# |||| TIMESTA 821 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
937 # | | | |||| | 822 # | | | |||| | |
938 bash-1977 [000] .... 17284.9936 823 bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath
939 bash-1977 [000] .... 17284.9936 824 bash-1977 [000] .... 17284.993653: __close_fd <-sys_close
940 bash-1977 [000] .... 17284.9936 825 bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd
941 sshd-1974 [003] .... 17284.9936 826 sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
942 bash-1977 [000] .... 17284.9936 827 bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
943 bash-1977 [000] ...1 17284.9936 828 bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
944 bash-1977 [000] ...1 17284.9936 829 bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
945 bash-1977 [000] .... 17284.9936 830 bash-1977 [000] .... 17284.993657: filp_close <-__close_fd
946 bash-1977 [000] .... 17284.9936 831 bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close
947 sshd-1974 [003] .... 17284.9936 832 sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath
948 .... 833 ....
949 834
950 A header is printed with the tracer name that 835 A header is printed with the tracer name that is represented by
951 the trace. In this case the tracer is "functio 836 the trace. In this case the tracer is "function". Then it shows the
952 number of events in the buffer as well as the 837 number of events in the buffer as well as the total number of entries
953 that were written. The difference is the numbe 838 that were written. The difference is the number of entries that were
954 lost due to the buffer filling up (250280 - 14 839 lost due to the buffer filling up (250280 - 140080 = 110200 events
955 lost). 840 lost).
956 841
957 The header explains the content of the events. 842 The header explains the content of the events. Task name "bash", the task
958 PID "1977", the CPU that it was running on "00 843 PID "1977", the CPU that it was running on "000", the latency format
959 (explained below), the timestamp in <secs>.<us 844 (explained below), the timestamp in <secs>.<usecs> format, the
960 function name that was traced "sys_close" and 845 function name that was traced "sys_close" and the parent function that
961 called this function "system_call_fastpath". T 846 called this function "system_call_fastpath". The timestamp is the time
962 at which the function was entered. 847 at which the function was entered.
963 848
964 Latency trace format 849 Latency trace format
965 -------------------- 850 --------------------
966 851
967 When the latency-format option is enabled or w 852 When the latency-format option is enabled or when one of the latency
968 tracers is set, the trace file gives somewhat 853 tracers is set, the trace file gives somewhat more information to see
969 why a latency happened. Here is a typical trac 854 why a latency happened. Here is a typical trace::
970 855
971 # tracer: irqsoff 856 # tracer: irqsoff
972 # 857 #
973 # irqsoff latency trace v1.1.5 on 3.8.0-test 858 # irqsoff latency trace v1.1.5 on 3.8.0-test+
974 # ------------------------------------------ 859 # --------------------------------------------------------------------
975 # latency: 259 us, #4/4, CPU#2 | (M:preempt 860 # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
976 # ----------------- 861 # -----------------
977 # | task: ps-6143 (uid:0 nice:0 policy:0 862 # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
978 # ----------------- 863 # -----------------
979 # => started at: __lock_task_sighand 864 # => started at: __lock_task_sighand
980 # => ended at: _raw_spin_unlock_irqrestor 865 # => ended at: _raw_spin_unlock_irqrestore
981 # 866 #
982 # 867 #
983 # _------=> CPU# 868 # _------=> CPU#
984 # / _-----=> irqs-off 869 # / _-----=> irqs-off
985 # | / _----=> need-resched 870 # | / _----=> need-resched
986 # || / _---=> hardirq/softirq 871 # || / _---=> hardirq/softirq
987 # ||| / _--=> preempt-depth 872 # ||| / _--=> preempt-depth
988 # |||| / delay 873 # |||| / delay
989 # cmd pid ||||| time | caller 874 # cmd pid ||||| time | caller
990 # \ / ||||| \ | / 875 # \ / ||||| \ | /
991 ps-6143 2d... 0us!: trace_hardir 876 ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand
992 ps-6143 2d..1 259us+: trace_hardir 877 ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
993 ps-6143 2d..1 263us+: time_hardirq 878 ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
994 ps-6143 2d..1 306us : <stack trace 879 ps-6143 2d..1 306us : <stack trace>
995 => trace_hardirqs_on_caller 880 => trace_hardirqs_on_caller
996 => trace_hardirqs_on 881 => trace_hardirqs_on
997 => _raw_spin_unlock_irqrestore 882 => _raw_spin_unlock_irqrestore
998 => do_task_stat 883 => do_task_stat
999 => proc_tgid_stat 884 => proc_tgid_stat
1000 => proc_single_show 885 => proc_single_show
1001 => seq_read 886 => seq_read
1002 => vfs_read 887 => vfs_read
1003 => sys_read 888 => sys_read
1004 => system_call_fastpath 889 => system_call_fastpath
1005 890
1006 891
1007 This shows that the current tracer is "irqsof 892 This shows that the current tracer is "irqsoff" tracing the time
1008 for which interrupts were disabled. It gives 893 for which interrupts were disabled. It gives the trace version (which
1009 never changes) and the version of the kernel 894 never changes) and the version of the kernel upon which this was executed on
1010 (3.8). Then it displays the max latency in mi 895 (3.8). Then it displays the max latency in microseconds (259 us). The number
1011 of trace entries displayed and the total numb 896 of trace entries displayed and the total number (both are four: #4/4).
1012 VP, KP, SP, and HP are always zero and are re 897 VP, KP, SP, and HP are always zero and are reserved for later use.
1013 #P is the number of online CPUs (#P:4). 898 #P is the number of online CPUs (#P:4).
1014 899
1015 The task is the process that was running when 900 The task is the process that was running when the latency
1016 occurred. (ps pid: 6143). 901 occurred. (ps pid: 6143).
1017 902
1018 The start and stop (the functions in which th 903 The start and stop (the functions in which the interrupts were
1019 disabled and enabled respectively) that cause 904 disabled and enabled respectively) that caused the latencies:
1020 905
1021 - __lock_task_sighand is where the interrup 906 - __lock_task_sighand is where the interrupts were disabled.
1022 - _raw_spin_unlock_irqrestore is where they 907 - _raw_spin_unlock_irqrestore is where they were enabled again.
1023 908
1024 The next lines after the header are the trace 909 The next lines after the header are the trace itself. The header
1025 explains which is which. 910 explains which is which.
1026 911
1027 cmd: The name of the process in the trace. 912 cmd: The name of the process in the trace.
1028 913
1029 pid: The PID of that process. 914 pid: The PID of that process.
1030 915
1031 CPU#: The CPU which the process was running 916 CPU#: The CPU which the process was running on.
1032 917
1033 irqs-off: 'd' interrupts are disabled. '.' 918 irqs-off: 'd' interrupts are disabled. '.' otherwise.
1034 .. caution:: If the architecture does 919 .. caution:: If the architecture does not support a way to
1035 read the irq flags variable, 920 read the irq flags variable, an 'X' will always
1036 be printed here. 921 be printed here.
1037 922
1038 need-resched: 923 need-resched:
1039 - 'N' both TIF_NEED_RESCHED and PREEM 924 - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
1040 - 'n' only TIF_NEED_RESCHED is set, 925 - 'n' only TIF_NEED_RESCHED is set,
1041 - 'p' only PREEMPT_NEED_RESCHED is se 926 - 'p' only PREEMPT_NEED_RESCHED is set,
1042 - '.' otherwise. 927 - '.' otherwise.
1043 928
1044 hardirq/softirq: 929 hardirq/softirq:
1045 - 'Z' - NMI occurred inside a hardirq 930 - 'Z' - NMI occurred inside a hardirq
1046 - 'z' - NMI is running 931 - 'z' - NMI is running
1047 - 'H' - hard irq occurred inside a so 932 - 'H' - hard irq occurred inside a softirq.
1048 - 'h' - hard irq is running 933 - 'h' - hard irq is running
1049 - 's' - soft irq is running 934 - 's' - soft irq is running
1050 - '.' - normal context. 935 - '.' - normal context.
1051 936
1052 preempt-depth: The level of preempt_disable 937 preempt-depth: The level of preempt_disabled
1053 938
1054 The above is mostly meaningful for kernel dev 939 The above is mostly meaningful for kernel developers.
1055 940
1056 time: 941 time:
1057 When the latency-format option is ena 942 When the latency-format option is enabled, the trace file
1058 output includes a timestamp relative 943 output includes a timestamp relative to the start of the
1059 trace. This differs from the output w 944 trace. This differs from the output when latency-format
1060 is disabled, which includes an absolu 945 is disabled, which includes an absolute timestamp.
1061 946
1062 delay: 947 delay:
1063 This is just to help catch your eye a 948 This is just to help catch your eye a bit better. And
1064 needs to be fixed to be only relative 949 needs to be fixed to be only relative to the same CPU.
1065 The marks are determined by the diffe 950 The marks are determined by the difference between this
1066 current trace and the next trace. 951 current trace and the next trace.
1067 952
1068 - '$' - greater than 1 second 953 - '$' - greater than 1 second
1069 - '@' - greater than 100 millisecon 954 - '@' - greater than 100 millisecond
1070 - '*' - greater than 10 millisecond 955 - '*' - greater than 10 millisecond
1071 - '#' - greater than 1000 microseco 956 - '#' - greater than 1000 microsecond
1072 - '!' - greater than 100 microsecon 957 - '!' - greater than 100 microsecond
1073 - '+' - greater than 10 microsecond 958 - '+' - greater than 10 microsecond
1074 - ' ' - less than or equal to 10 mi 959 - ' ' - less than or equal to 10 microsecond.
1075 960
1076 The rest is the same as the 'trace' file. 961 The rest is the same as the 'trace' file.
1077 962
1078 Note, the latency tracers will usually end 963 Note, the latency tracers will usually end with a back trace
1079 to easily find where the latency occurred. 964 to easily find where the latency occurred.
1080 965
1081 trace_options 966 trace_options
1082 ------------- 967 -------------
1083 968
1084 The trace_options file (or the options direct 969 The trace_options file (or the options directory) is used to control
1085 what gets printed in the trace output, or man 970 what gets printed in the trace output, or manipulate the tracers.
1086 To see what is available, simply cat the file 971 To see what is available, simply cat the file::
1087 972
1088 cat trace_options 973 cat trace_options
1089 print-parent 974 print-parent
1090 nosym-offset 975 nosym-offset
1091 nosym-addr 976 nosym-addr
1092 noverbose 977 noverbose
1093 noraw 978 noraw
1094 nohex 979 nohex
1095 nobin 980 nobin
1096 noblock 981 noblock
1097 nofields <<
1098 trace_printk 982 trace_printk
1099 annotate 983 annotate
1100 nouserstacktrace 984 nouserstacktrace
1101 nosym-userobj 985 nosym-userobj
1102 noprintk-msg-only 986 noprintk-msg-only
1103 context-info 987 context-info
1104 nolatency-format 988 nolatency-format
1105 record-cmd 989 record-cmd
1106 norecord-tgid 990 norecord-tgid
1107 overwrite 991 overwrite
1108 nodisable_on_free 992 nodisable_on_free
1109 irq-info 993 irq-info
1110 markers 994 markers
1111 noevent-fork 995 noevent-fork
1112 function-trace 996 function-trace
1113 nofunction-fork 997 nofunction-fork
1114 nodisplay-graph 998 nodisplay-graph
1115 nostacktrace 999 nostacktrace
1116 nobranch 1000 nobranch
1117 1001
1118 To disable one of the options, echo in the op 1002 To disable one of the options, echo in the option prepended with
1119 "no":: 1003 "no"::
1120 1004
1121 echo noprint-parent > trace_options 1005 echo noprint-parent > trace_options
1122 1006
1123 To enable an option, leave off the "no":: 1007 To enable an option, leave off the "no"::
1124 1008
1125 echo sym-offset > trace_options 1009 echo sym-offset > trace_options
1126 1010
1127 Here are the available options: 1011 Here are the available options:
1128 1012
1129 print-parent 1013 print-parent
1130 On function traces, display the calli 1014 On function traces, display the calling (parent)
1131 function as well as the function bein 1015 function as well as the function being traced.
1132 :: 1016 ::
1133 1017
1134 print-parent: 1018 print-parent:
1135 bash-4000 [01] 1477.606694: simp 1019 bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul
1136 1020
1137 noprint-parent: 1021 noprint-parent:
1138 bash-4000 [01] 1477.606694: simp 1022 bash-4000 [01] 1477.606694: simple_strtoul
1139 1023
1140 1024
1141 sym-offset 1025 sym-offset
1142 Display not only the function name, b 1026 Display not only the function name, but also the
1143 offset in the function. For example, 1027 offset in the function. For example, instead of
1144 seeing just "ktime_get", you will see 1028 seeing just "ktime_get", you will see
1145 "ktime_get+0xb/0x20". 1029 "ktime_get+0xb/0x20".
1146 :: 1030 ::
1147 1031
1148 sym-offset: 1032 sym-offset:
1149 bash-4000 [01] 1477.606694: simp 1033 bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
1150 1034
1151 sym-addr 1035 sym-addr
1152 This will also display the function a 1036 This will also display the function address as well
1153 as the function name. 1037 as the function name.
1154 :: 1038 ::
1155 1039
1156 sym-addr: 1040 sym-addr:
1157 bash-4000 [01] 1477.606694: simp 1041 bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
1158 1042
1159 verbose 1043 verbose
1160 This deals with the trace file when t 1044 This deals with the trace file when the
1161 latency-format option is enabled. 1045 latency-format option is enabled.
1162 :: 1046 ::
1163 1047
1164 bash 4000 1 0 00000000 00010a95 1048 bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
1165 (+0.000ms): simple_strtoul (kstrt 1049 (+0.000ms): simple_strtoul (kstrtoul)
1166 1050
1167 raw 1051 raw
1168 This will display raw numbers. This o 1052 This will display raw numbers. This option is best for
1169 use with user applications that can t 1053 use with user applications that can translate the raw
1170 numbers better than having it done in 1054 numbers better than having it done in the kernel.
1171 1055
1172 hex 1056 hex
1173 Similar to raw, but the numbers will 1057 Similar to raw, but the numbers will be in a hexadecimal format.
1174 1058
1175 bin 1059 bin
1176 This will print out the formats in ra 1060 This will print out the formats in raw binary.
1177 1061
1178 block 1062 block
1179 When set, reading trace_pipe will not 1063 When set, reading trace_pipe will not block when polled.
1180 1064
1181 fields <<
1182 Print the fields as described by thei <<
1183 option than using hex, bin or raw, as <<
1184 of the content of the event. <<
1185 <<
1186 trace_printk 1065 trace_printk
1187 Can disable trace_printk() from writi 1066 Can disable trace_printk() from writing into the buffer.
1188 1067
1189 trace_printk_dest <<
1190 Set to have trace_printk() and simila <<
1191 write into this instance. Note, only <<
1192 this set. By setting this flag, it cl <<
1193 of the instance that had it set previ <<
1194 level trace has this set, and will ge <<
1195 instance has it set then clears it. <<
1196 <<
1197 This flag cannot be cleared by the to <<
1198 default instance. The only way the to <<
1199 cleared, is by it being set in anothe <<
1200 <<
1201 annotate 1068 annotate
1202 It is sometimes confusing when the CP 1069 It is sometimes confusing when the CPU buffers are full
1203 and one CPU buffer had a lot of event 1070 and one CPU buffer had a lot of events recently, thus
1204 a shorter time frame, were another CP 1071 a shorter time frame, were another CPU may have only had
1205 a few events, which lets it have olde 1072 a few events, which lets it have older events. When
1206 the trace is reported, it shows the o 1073 the trace is reported, it shows the oldest events first,
1207 and it may look like only one CPU ran 1074 and it may look like only one CPU ran (the one with the
1208 oldest events). When the annotate opt 1075 oldest events). When the annotate option is set, it will
1209 display when a new CPU buffer started 1076 display when a new CPU buffer started::
1210 1077
1211 <idle>-0 [001] 1078 <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
1212 <idle>-0 [001] 1079 <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
1213 <idle>-0 [001] 1080 <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
1214 ##### CPU 2 buffer started ## 1081 ##### CPU 2 buffer started ####
1215 <idle>-0 [002] 1082 <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
1216 <idle>-0 [001] 1083 <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
1217 <idle>-0 [001] 1084 <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
1218 1085
1219 userstacktrace 1086 userstacktrace
1220 This option changes the trace. It rec 1087 This option changes the trace. It records a
1221 stacktrace of the current user space 1088 stacktrace of the current user space thread after
1222 each trace event. 1089 each trace event.
1223 1090
1224 sym-userobj 1091 sym-userobj
1225 when user stacktrace are enabled, loo 1092 when user stacktrace are enabled, look up which
1226 object the address belongs to, and pr 1093 object the address belongs to, and print a
1227 relative address. This is especially 1094 relative address. This is especially useful when
1228 ASLR is on, otherwise you don't get a 1095 ASLR is on, otherwise you don't get a chance to
1229 resolve the address to object/file/li 1096 resolve the address to object/file/line after
1230 the app is no longer running 1097 the app is no longer running
1231 1098
1232 The lookup is performed when you read 1099 The lookup is performed when you read
1233 trace,trace_pipe. Example:: 1100 trace,trace_pipe. Example::
1234 1101
1235 a.out-1623 [000] 40874.465 1102 a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
1236 x494] <- /root/a.out[+0x4a8 1103 x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
1237 1104
1238 1105
1239 printk-msg-only 1106 printk-msg-only
1240 When set, trace_printk()s will only s 1107 When set, trace_printk()s will only show the format
1241 and not their parameters (if trace_bp 1108 and not their parameters (if trace_bprintk() or
1242 trace_bputs() was used to save the tr 1109 trace_bputs() was used to save the trace_printk()).
1243 1110
1244 context-info 1111 context-info
1245 Show only the event data. Hides the c 1112 Show only the event data. Hides the comm, PID,
1246 timestamp, CPU, and other useful data 1113 timestamp, CPU, and other useful data.
1247 1114
1248 latency-format 1115 latency-format
1249 This option changes the trace output. 1116 This option changes the trace output. When it is enabled,
1250 the trace displays additional informa 1117 the trace displays additional information about the
1251 latency, as described in "Latency tra 1118 latency, as described in "Latency trace format".
1252 1119
1253 pause-on-trace <<
1254 When set, opening the trace file for <<
1255 writing to the ring buffer (as if tra <<
1256 This simulates the original behavior <<
1257 When the file is closed, tracing will <<
1258 <<
1259 hash-ptr <<
1260 When set, "%p" in the event printk fo <<
1261 hashed pointer value instead of real <<
1262 This will be useful if you want to fi <<
1263 value is corresponding to the real va <<
1264 <<
1265 record-cmd 1120 record-cmd
1266 When any event or tracer is enabled, 1121 When any event or tracer is enabled, a hook is enabled
1267 in the sched_switch trace point to fi 1122 in the sched_switch trace point to fill comm cache
1268 with mapped pids and comms. But this 1123 with mapped pids and comms. But this may cause some
1269 overhead, and if you only care about 1124 overhead, and if you only care about pids, and not the
1270 name of the task, disabling this opti 1125 name of the task, disabling this option can lower the
1271 impact of tracing. See "saved_cmdline 1126 impact of tracing. See "saved_cmdlines".
1272 1127
1273 record-tgid 1128 record-tgid
1274 When any event or tracer is enabled, 1129 When any event or tracer is enabled, a hook is enabled
1275 in the sched_switch trace point to fi 1130 in the sched_switch trace point to fill the cache of
1276 mapped Thread Group IDs (TGID) mappin 1131 mapped Thread Group IDs (TGID) mapping to pids. See
1277 "saved_tgids". 1132 "saved_tgids".
1278 1133
1279 overwrite 1134 overwrite
1280 This controls what happens when the t 1135 This controls what happens when the trace buffer is
1281 full. If "1" (default), the oldest ev 1136 full. If "1" (default), the oldest events are
1282 discarded and overwritten. If "0", th 1137 discarded and overwritten. If "0", then the newest
1283 events are discarded. 1138 events are discarded.
1284 (see per_cpu/cpu0/stats for overrun a 1139 (see per_cpu/cpu0/stats for overrun and dropped)
1285 1140
1286 disable_on_free 1141 disable_on_free
1287 When the free_buffer is closed, traci 1142 When the free_buffer is closed, tracing will
1288 stop (tracing_on set to 0). 1143 stop (tracing_on set to 0).
1289 1144
1290 irq-info 1145 irq-info
1291 Shows the interrupt, preempt count, n 1146 Shows the interrupt, preempt count, need resched data.
1292 When disabled, the trace looks like:: 1147 When disabled, the trace looks like::
1293 1148
1294 # tracer: function 1149 # tracer: function
1295 # 1150 #
1296 # entries-in-buffer/entries-w 1151 # entries-in-buffer/entries-written: 144405/9452052 #P:4
1297 # 1152 #
1298 # TASK-PID CPU# 1153 # TASK-PID CPU# TIMESTAMP FUNCTION
1299 # | | | 1154 # | | | | |
1300 <idle>-0 [002] 1155 <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
1301 <idle>-0 [002] 1156 <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89
1302 <idle>-0 [002] 1157 <idle>-0 [002] 23636.756055: enqueue_task <-activate_task
1303 1158
1304 1159
1305 markers 1160 markers
1306 When set, the trace_marker is writabl 1161 When set, the trace_marker is writable (only by root).
1307 When disabled, the trace_marker will 1162 When disabled, the trace_marker will error with EINVAL
1308 on write. 1163 on write.
1309 1164
1310 event-fork 1165 event-fork
1311 When set, tasks with PIDs listed in s 1166 When set, tasks with PIDs listed in set_event_pid will have
1312 the PIDs of their children added to s 1167 the PIDs of their children added to set_event_pid when those
1313 tasks fork. Also, when tasks with PID 1168 tasks fork. Also, when tasks with PIDs in set_event_pid exit,
1314 their PIDs will be removed from the f 1169 their PIDs will be removed from the file.
1315 1170
1316 This affects PIDs listed in set_event <<
1317 <<
1318 function-trace 1171 function-trace
1319 The latency tracers will enable funct 1172 The latency tracers will enable function tracing
1320 if this option is enabled (default it 1173 if this option is enabled (default it is). When
1321 it is disabled, the latency tracers d 1174 it is disabled, the latency tracers do not trace
1322 functions. This keeps the overhead of 1175 functions. This keeps the overhead of the tracer down
1323 when performing latency tests. 1176 when performing latency tests.
1324 1177
1325 function-fork 1178 function-fork
1326 When set, tasks with PIDs listed in s 1179 When set, tasks with PIDs listed in set_ftrace_pid will
1327 have the PIDs of their children added 1180 have the PIDs of their children added to set_ftrace_pid
1328 when those tasks fork. Also, when tas 1181 when those tasks fork. Also, when tasks with PIDs in
1329 set_ftrace_pid exit, their PIDs will 1182 set_ftrace_pid exit, their PIDs will be removed from the
1330 file. 1183 file.
1331 1184
1332 This affects PIDs in set_ftrace_notra <<
1333 <<
1334 display-graph 1185 display-graph
1335 When set, the latency tracers (irqsof 1186 When set, the latency tracers (irqsoff, wakeup, etc) will
1336 use function graph tracing instead of 1187 use function graph tracing instead of function tracing.
1337 1188
1338 stacktrace 1189 stacktrace
1339 When set, a stack trace is recorded a 1190 When set, a stack trace is recorded after any trace event
1340 is recorded. 1191 is recorded.
1341 1192
1342 branch 1193 branch
1343 Enable branch tracing with the tracer 1194 Enable branch tracing with the tracer. This enables branch
1344 tracer along with the currently set t 1195 tracer along with the currently set tracer. Enabling this
1345 with the "nop" tracer is the same as 1196 with the "nop" tracer is the same as just enabling the
1346 "branch" tracer. 1197 "branch" tracer.
1347 1198
1348 .. tip:: Some tracers have their own options. 1199 .. tip:: Some tracers have their own options. They only appear in this
1349 file when the tracer is active. They a 1200 file when the tracer is active. They always appear in the
1350 options directory. 1201 options directory.
1351 1202
1352 1203
1353 Here are the per tracer options: 1204 Here are the per tracer options:
1354 1205
1355 Options for function tracer: 1206 Options for function tracer:
1356 1207
1357 func_stack_trace 1208 func_stack_trace
1358 When set, a stack trace is recorded a 1209 When set, a stack trace is recorded after every
1359 function that is recorded. NOTE! Limi 1210 function that is recorded. NOTE! Limit the functions
1360 that are recorded before enabling thi 1211 that are recorded before enabling this, with
1361 "set_ftrace_filter" otherwise the sys 1212 "set_ftrace_filter" otherwise the system performance
1362 will be critically degraded. Remember 1213 will be critically degraded. Remember to disable
1363 this option before clearing the funct 1214 this option before clearing the function filter.
1364 1215
1365 Options for function_graph tracer: 1216 Options for function_graph tracer:
1366 1217
1367 Since the function_graph tracer has a slight 1218 Since the function_graph tracer has a slightly different output
1368 it has its own options to control what is di 1219 it has its own options to control what is displayed.
1369 1220
1370 funcgraph-overrun 1221 funcgraph-overrun
1371 When set, the "overrun" of the graph 1222 When set, the "overrun" of the graph stack is
1372 displayed after each function traced. 1223 displayed after each function traced. The
1373 overrun, is when the stack depth of t 1224 overrun, is when the stack depth of the calls
1374 is greater than what is reserved for 1225 is greater than what is reserved for each task.
1375 Each task has a fixed array of functi 1226 Each task has a fixed array of functions to
1376 trace in the call graph. If the depth 1227 trace in the call graph. If the depth of the
1377 calls exceeds that, the function is n 1228 calls exceeds that, the function is not traced.
1378 The overrun is the number of function 1229 The overrun is the number of functions missed
1379 due to exceeding this array. 1230 due to exceeding this array.
1380 1231
1381 funcgraph-cpu 1232 funcgraph-cpu
1382 When set, the CPU number of the CPU w 1233 When set, the CPU number of the CPU where the trace
1383 occurred is displayed. 1234 occurred is displayed.
1384 1235
1385 funcgraph-overhead 1236 funcgraph-overhead
1386 When set, if the function takes longe 1237 When set, if the function takes longer than
1387 A certain amount, then a delay marker 1238 A certain amount, then a delay marker is
1388 displayed. See "delay" above, under t 1239 displayed. See "delay" above, under the
1389 header description. 1240 header description.
1390 1241
1391 funcgraph-proc 1242 funcgraph-proc
1392 Unlike other tracers, the process' co 1243 Unlike other tracers, the process' command line
1393 is not displayed by default, but inst 1244 is not displayed by default, but instead only
1394 when a task is traced in and out duri 1245 when a task is traced in and out during a context
1395 switch. Enabling this options has the 1246 switch. Enabling this options has the command
1396 of each process displayed at every li 1247 of each process displayed at every line.
1397 1248
1398 funcgraph-duration 1249 funcgraph-duration
1399 At the end of each function (the retu 1250 At the end of each function (the return)
1400 the duration of the amount of time in 1251 the duration of the amount of time in the
1401 function is displayed in microseconds 1252 function is displayed in microseconds.
1402 1253
1403 funcgraph-abstime 1254 funcgraph-abstime
1404 When set, the timestamp is displayed 1255 When set, the timestamp is displayed at each line.
1405 1256
1406 funcgraph-irqs 1257 funcgraph-irqs
1407 When disabled, functions that happen 1258 When disabled, functions that happen inside an
1408 interrupt will not be traced. 1259 interrupt will not be traced.
1409 1260
1410 funcgraph-tail 1261 funcgraph-tail
1411 When set, the return event will inclu 1262 When set, the return event will include the function
1412 that it represents. By default this i 1263 that it represents. By default this is off, and
1413 only a closing curly bracket "}" is d 1264 only a closing curly bracket "}" is displayed for
1414 the return of a function. 1265 the return of a function.
1415 1266
1416 funcgraph-retval <<
1417 When set, the return value of each tr <<
1418 will be printed after an equal sign " <<
1419 this is off. <<
1420 <<
1421 funcgraph-retval-hex <<
1422 When set, the return value will alway <<
1423 in hexadecimal format. If the option <<
1424 the return value is an error code, it <<
1425 in signed decimal format; otherwise i <<
1426 printed in hexadecimal format. By def <<
1427 is off. <<
1428 <<
1429 sleep-time 1267 sleep-time
1430 When running function graph tracer, t 1268 When running function graph tracer, to include
1431 the time a task schedules out in its 1269 the time a task schedules out in its function.
1432 When enabled, it will account time th 1270 When enabled, it will account time the task has been
1433 scheduled out as part of the function 1271 scheduled out as part of the function call.
1434 1272
1435 graph-time 1273 graph-time
1436 When running function profiler with f 1274 When running function profiler with function graph tracer,
1437 to include the time to call nested fu 1275 to include the time to call nested functions. When this is
1438 not set, the time reported for the fu 1276 not set, the time reported for the function will only
1439 include the time the function itself 1277 include the time the function itself executed for, not the
1440 time for functions that it called. 1278 time for functions that it called.
1441 1279
1442 Options for blk tracer: 1280 Options for blk tracer:
1443 1281
1444 blk_classic 1282 blk_classic
1445 Shows a more minimalistic output. 1283 Shows a more minimalistic output.
1446 1284
1447 1285
1448 irqsoff 1286 irqsoff
1449 ------- 1287 -------
1450 1288
1451 When interrupts are disabled, the CPU can not 1289 When interrupts are disabled, the CPU can not react to any other
1452 external event (besides NMIs and SMIs). This 1290 external event (besides NMIs and SMIs). This prevents the timer
1453 interrupt from triggering or the mouse interr 1291 interrupt from triggering or the mouse interrupt from letting
1454 the kernel know of a new mouse event. The res 1292 the kernel know of a new mouse event. The result is a latency
1455 with the reaction time. 1293 with the reaction time.
1456 1294
1457 The irqsoff tracer tracks the time for which 1295 The irqsoff tracer tracks the time for which interrupts are
1458 disabled. When a new maximum latency is hit, 1296 disabled. When a new maximum latency is hit, the tracer saves
1459 the trace leading up to that latency point so 1297 the trace leading up to that latency point so that every time a
1460 new maximum is reached, the old saved trace i 1298 new maximum is reached, the old saved trace is discarded and the
1461 new trace is saved. 1299 new trace is saved.
1462 1300
1463 To reset the maximum, echo 0 into tracing_max 1301 To reset the maximum, echo 0 into tracing_max_latency. Here is
1464 an example:: 1302 an example::
1465 1303
1466 # echo 0 > options/function-trace 1304 # echo 0 > options/function-trace
1467 # echo irqsoff > current_tracer 1305 # echo irqsoff > current_tracer
1468 # echo 1 > tracing_on 1306 # echo 1 > tracing_on
1469 # echo 0 > tracing_max_latency 1307 # echo 0 > tracing_max_latency
1470 # ls -ltr 1308 # ls -ltr
1471 [...] 1309 [...]
1472 # echo 0 > tracing_on 1310 # echo 0 > tracing_on
1473 # cat trace 1311 # cat trace
1474 # tracer: irqsoff 1312 # tracer: irqsoff
1475 # 1313 #
1476 # irqsoff latency trace v1.1.5 on 3.8.0-tes 1314 # irqsoff latency trace v1.1.5 on 3.8.0-test+
1477 # ----------------------------------------- 1315 # --------------------------------------------------------------------
1478 # latency: 16 us, #4/4, CPU#0 | (M:preempt 1316 # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1479 # ----------------- 1317 # -----------------
1480 # | task: swapper/0-0 (uid:0 nice:0 poli 1318 # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
1481 # ----------------- 1319 # -----------------
1482 # => started at: run_timer_softirq 1320 # => started at: run_timer_softirq
1483 # => ended at: run_timer_softirq 1321 # => ended at: run_timer_softirq
1484 # 1322 #
1485 # 1323 #
1486 # _------=> CPU# 1324 # _------=> CPU#
1487 # / _-----=> irqs-off 1325 # / _-----=> irqs-off
1488 # | / _----=> need-resched 1326 # | / _----=> need-resched
1489 # || / _---=> hardirq/softir 1327 # || / _---=> hardirq/softirq
1490 # ||| / _--=> preempt-depth 1328 # ||| / _--=> preempt-depth
1491 # |||| / delay 1329 # |||| / delay
1492 # cmd pid ||||| time | caller 1330 # cmd pid ||||| time | caller
1493 # \ / ||||| \ | / 1331 # \ / ||||| \ | /
1494 <idle>-0 0d.s2 0us+: _raw_spin_l 1332 <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq
1495 <idle>-0 0dNs3 17us : _raw_spin_u 1333 <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq
1496 <idle>-0 0dNs3 17us+: trace_hardi 1334 <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq
1497 <idle>-0 0dNs3 25us : <stack trac 1335 <idle>-0 0dNs3 25us : <stack trace>
1498 => _raw_spin_unlock_irq 1336 => _raw_spin_unlock_irq
1499 => run_timer_softirq 1337 => run_timer_softirq
1500 => __do_softirq 1338 => __do_softirq
1501 => call_softirq 1339 => call_softirq
1502 => do_softirq 1340 => do_softirq
1503 => irq_exit 1341 => irq_exit
1504 => smp_apic_timer_interrupt 1342 => smp_apic_timer_interrupt
1505 => apic_timer_interrupt 1343 => apic_timer_interrupt
1506 => rcu_idle_exit 1344 => rcu_idle_exit
1507 => cpu_idle 1345 => cpu_idle
1508 => rest_init 1346 => rest_init
1509 => start_kernel 1347 => start_kernel
1510 => x86_64_start_reservations 1348 => x86_64_start_reservations
1511 => x86_64_start_kernel 1349 => x86_64_start_kernel
1512 1350
1513 Here we see that we had a latency of 16 micro !! 1351 Here we see that that we had a latency of 16 microseconds (which is
1514 very good). The _raw_spin_lock_irq in run_tim 1352 very good). The _raw_spin_lock_irq in run_timer_softirq disabled
1515 interrupts. The difference between the 16 and 1353 interrupts. The difference between the 16 and the displayed
1516 timestamp 25us occurred because the clock was 1354 timestamp 25us occurred because the clock was incremented
1517 between the time of recording the max latency 1355 between the time of recording the max latency and the time of
1518 recording the function that had that latency. 1356 recording the function that had that latency.
1519 1357
1520 Note the above example had function-trace not 1358 Note the above example had function-trace not set. If we set
1521 function-trace, we get a much larger output:: 1359 function-trace, we get a much larger output::
1522 1360
1523 with echo 1 > options/function-trace 1361 with echo 1 > options/function-trace
1524 1362
1525 # tracer: irqsoff 1363 # tracer: irqsoff
1526 # 1364 #
1527 # irqsoff latency trace v1.1.5 on 3.8.0-tes 1365 # irqsoff latency trace v1.1.5 on 3.8.0-test+
1528 # ----------------------------------------- 1366 # --------------------------------------------------------------------
1529 # latency: 71 us, #168/168, CPU#3 | (M:pree 1367 # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1530 # ----------------- 1368 # -----------------
1531 # | task: bash-2042 (uid:0 nice:0 policy 1369 # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
1532 # ----------------- 1370 # -----------------
1533 # => started at: ata_scsi_queuecmd 1371 # => started at: ata_scsi_queuecmd
1534 # => ended at: ata_scsi_queuecmd 1372 # => ended at: ata_scsi_queuecmd
1535 # 1373 #
1536 # 1374 #
1537 # _------=> CPU# 1375 # _------=> CPU#
1538 # / _-----=> irqs-off 1376 # / _-----=> irqs-off
1539 # | / _----=> need-resched 1377 # | / _----=> need-resched
1540 # || / _---=> hardirq/softir 1378 # || / _---=> hardirq/softirq
1541 # ||| / _--=> preempt-depth 1379 # ||| / _--=> preempt-depth
1542 # |||| / delay 1380 # |||| / delay
1543 # cmd pid ||||| time | caller 1381 # cmd pid ||||| time | caller
1544 # \ / ||||| \ | / 1382 # \ / ||||| \ | /
1545 bash-2042 3d... 0us : _raw_spin_l 1383 bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
1546 bash-2042 3d... 0us : add_preempt 1384 bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave
1547 bash-2042 3d..1 1us : ata_scsi_fi 1385 bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd
1548 bash-2042 3d..1 1us : __ata_scsi_ 1386 bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev
1549 bash-2042 3d..1 2us : ata_find_de 1387 bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
1550 bash-2042 3d..1 2us : ata_qc_new_ 1388 bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd
1551 bash-2042 3d..1 3us : ata_sg_init 1389 bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd
1552 bash-2042 3d..1 4us : ata_scsi_rw 1390 bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
1553 bash-2042 3d..1 4us : ata_build_r 1391 bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat
1554 [...] 1392 [...]
1555 bash-2042 3d..1 67us : delay_tsc < 1393 bash-2042 3d..1 67us : delay_tsc <-__delay
1556 bash-2042 3d..1 67us : add_preempt 1394 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1557 bash-2042 3d..2 67us : sub_preempt 1395 bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc
1558 bash-2042 3d..1 67us : add_preempt 1396 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1559 bash-2042 3d..2 68us : sub_preempt 1397 bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc
1560 bash-2042 3d..1 68us+: ata_bmdma_s 1398 bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue
1561 bash-2042 3d..1 71us : _raw_spin_u 1399 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1562 bash-2042 3d..1 71us : _raw_spin_u 1400 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1563 bash-2042 3d..1 72us+: trace_hardi 1401 bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd
1564 bash-2042 3d..1 120us : <stack trac 1402 bash-2042 3d..1 120us : <stack trace>
1565 => _raw_spin_unlock_irqrestore 1403 => _raw_spin_unlock_irqrestore
1566 => ata_scsi_queuecmd 1404 => ata_scsi_queuecmd
1567 => scsi_dispatch_cmd 1405 => scsi_dispatch_cmd
1568 => scsi_request_fn 1406 => scsi_request_fn
1569 => __blk_run_queue_uncond 1407 => __blk_run_queue_uncond
1570 => __blk_run_queue 1408 => __blk_run_queue
1571 => blk_queue_bio 1409 => blk_queue_bio
1572 => submit_bio_noacct !! 1410 => generic_make_request
1573 => submit_bio 1411 => submit_bio
1574 => submit_bh 1412 => submit_bh
1575 => __ext3_get_inode_loc 1413 => __ext3_get_inode_loc
1576 => ext3_iget 1414 => ext3_iget
1577 => ext3_lookup 1415 => ext3_lookup
1578 => lookup_real 1416 => lookup_real
1579 => __lookup_hash 1417 => __lookup_hash
1580 => walk_component 1418 => walk_component
1581 => lookup_last 1419 => lookup_last
1582 => path_lookupat 1420 => path_lookupat
1583 => filename_lookup 1421 => filename_lookup
1584 => user_path_at_empty 1422 => user_path_at_empty
1585 => user_path_at 1423 => user_path_at
1586 => vfs_fstatat 1424 => vfs_fstatat
1587 => vfs_stat 1425 => vfs_stat
1588 => sys_newstat 1426 => sys_newstat
1589 => system_call_fastpath 1427 => system_call_fastpath
1590 1428
1591 1429
1592 Here we traced a 71 microsecond latency. But 1430 Here we traced a 71 microsecond latency. But we also see all the
1593 functions that were called during that time. 1431 functions that were called during that time. Note that by
1594 enabling function tracing, we incur an added 1432 enabling function tracing, we incur an added overhead. This
1595 overhead may extend the latency times. But ne 1433 overhead may extend the latency times. But nevertheless, this
1596 trace has provided some very helpful debuggin 1434 trace has provided some very helpful debugging information.
1597 1435
1598 If we prefer function graph output instead of 1436 If we prefer function graph output instead of function, we can set
1599 display-graph option:: 1437 display-graph option::
1600 1438
1601 with echo 1 > options/display-graph 1439 with echo 1 > options/display-graph
1602 1440
1603 # tracer: irqsoff 1441 # tracer: irqsoff
1604 # 1442 #
1605 # irqsoff latency trace v1.1.5 on 4.20.0-rc 1443 # irqsoff latency trace v1.1.5 on 4.20.0-rc6+
1606 # ----------------------------------------- 1444 # --------------------------------------------------------------------
1607 # latency: 3751 us, #274/274, CPU#0 | (M:de 1445 # latency: 3751 us, #274/274, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:4)
1608 # ----------------- 1446 # -----------------
1609 # | task: bash-1507 (uid:0 nice:0 policy 1447 # | task: bash-1507 (uid:0 nice:0 policy:0 rt_prio:0)
1610 # ----------------- 1448 # -----------------
1611 # => started at: free_debug_processing 1449 # => started at: free_debug_processing
1612 # => ended at: return_to_handler 1450 # => ended at: return_to_handler
1613 # 1451 #
1614 # 1452 #
1615 # _-- 1453 # _-----=> irqs-off
1616 # / _- 1454 # / _----=> need-resched
1617 # | / _ 1455 # | / _---=> hardirq/softirq
1618 # || / 1456 # || / _--=> preempt-depth
1619 # ||| / 1457 # ||| /
1620 # REL TIME CPU TASK/PID |||| 1458 # REL TIME CPU TASK/PID |||| DURATION FUNCTION CALLS
1621 # | | | | |||| 1459 # | | | | |||| | | | | | |
1622 0 us | 0) bash-1507 | d... 1460 0 us | 0) bash-1507 | d... | 0.000 us | _raw_spin_lock_irqsave();
1623 0 us | 0) bash-1507 | d..1 1461 0 us | 0) bash-1507 | d..1 | 0.378 us | do_raw_spin_trylock();
1624 1 us | 0) bash-1507 | d..2 1462 1 us | 0) bash-1507 | d..2 | | set_track() {
1625 2 us | 0) bash-1507 | d..2 1463 2 us | 0) bash-1507 | d..2 | | save_stack_trace() {
1626 2 us | 0) bash-1507 | d..2 1464 2 us | 0) bash-1507 | d..2 | | __save_stack_trace() {
1627 3 us | 0) bash-1507 | d..2 1465 3 us | 0) bash-1507 | d..2 | | __unwind_start() {
1628 3 us | 0) bash-1507 | d..2 1466 3 us | 0) bash-1507 | d..2 | | get_stack_info() {
1629 3 us | 0) bash-1507 | d..2 1467 3 us | 0) bash-1507 | d..2 | 0.351 us | in_task_stack();
1630 4 us | 0) bash-1507 | d..2 1468 4 us | 0) bash-1507 | d..2 | 1.107 us | }
1631 [...] 1469 [...]
1632 3750 us | 0) bash-1507 | d..1 1470 3750 us | 0) bash-1507 | d..1 | 0.516 us | do_raw_spin_unlock();
1633 3750 us | 0) bash-1507 | d..1 1471 3750 us | 0) bash-1507 | d..1 | 0.000 us | _raw_spin_unlock_irqrestore();
1634 3764 us | 0) bash-1507 | d..1 1472 3764 us | 0) bash-1507 | d..1 | 0.000 us | tracer_hardirqs_on();
1635 bash-1507 0d..1 3792us : <stack trac 1473 bash-1507 0d..1 3792us : <stack trace>
1636 => free_debug_processing 1474 => free_debug_processing
1637 => __slab_free 1475 => __slab_free
1638 => kmem_cache_free 1476 => kmem_cache_free
1639 => vm_area_free 1477 => vm_area_free
1640 => remove_vma 1478 => remove_vma
1641 => exit_mmap 1479 => exit_mmap
1642 => mmput 1480 => mmput
1643 => begin_new_exec !! 1481 => flush_old_exec
1644 => load_elf_binary 1482 => load_elf_binary
1645 => search_binary_handler 1483 => search_binary_handler
1646 => __do_execve_file.isra.32 1484 => __do_execve_file.isra.32
1647 => __x64_sys_execve 1485 => __x64_sys_execve
1648 => do_syscall_64 1486 => do_syscall_64
1649 => entry_SYSCALL_64_after_hwframe 1487 => entry_SYSCALL_64_after_hwframe
1650 1488
1651 preemptoff 1489 preemptoff
1652 ---------- 1490 ----------
1653 1491
1654 When preemption is disabled, we may be able t 1492 When preemption is disabled, we may be able to receive
1655 interrupts but the task cannot be preempted a 1493 interrupts but the task cannot be preempted and a higher
1656 priority task must wait for preemption to be 1494 priority task must wait for preemption to be enabled again
1657 before it can preempt a lower priority task. 1495 before it can preempt a lower priority task.
1658 1496
1659 The preemptoff tracer traces the places that 1497 The preemptoff tracer traces the places that disable preemption.
1660 Like the irqsoff tracer, it records the maxim 1498 Like the irqsoff tracer, it records the maximum latency for
1661 which preemption was disabled. The control of 1499 which preemption was disabled. The control of preemptoff tracer
1662 is much like the irqsoff tracer. 1500 is much like the irqsoff tracer.
1663 :: 1501 ::
1664 1502
1665 # echo 0 > options/function-trace 1503 # echo 0 > options/function-trace
1666 # echo preemptoff > current_tracer 1504 # echo preemptoff > current_tracer
1667 # echo 1 > tracing_on 1505 # echo 1 > tracing_on
1668 # echo 0 > tracing_max_latency 1506 # echo 0 > tracing_max_latency
1669 # ls -ltr 1507 # ls -ltr
1670 [...] 1508 [...]
1671 # echo 0 > tracing_on 1509 # echo 0 > tracing_on
1672 # cat trace 1510 # cat trace
1673 # tracer: preemptoff 1511 # tracer: preemptoff
1674 # 1512 #
1675 # preemptoff latency trace v1.1.5 on 3.8.0- 1513 # preemptoff latency trace v1.1.5 on 3.8.0-test+
1676 # ----------------------------------------- 1514 # --------------------------------------------------------------------
1677 # latency: 46 us, #4/4, CPU#1 | (M:preempt 1515 # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1678 # ----------------- 1516 # -----------------
1679 # | task: sshd-1991 (uid:0 nice:0 policy 1517 # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
1680 # ----------------- 1518 # -----------------
1681 # => started at: do_IRQ 1519 # => started at: do_IRQ
1682 # => ended at: do_IRQ 1520 # => ended at: do_IRQ
1683 # 1521 #
1684 # 1522 #
1685 # _------=> CPU# 1523 # _------=> CPU#
1686 # / _-----=> irqs-off 1524 # / _-----=> irqs-off
1687 # | / _----=> need-resched 1525 # | / _----=> need-resched
1688 # || / _---=> hardirq/softir 1526 # || / _---=> hardirq/softirq
1689 # ||| / _--=> preempt-depth 1527 # ||| / _--=> preempt-depth
1690 # |||| / delay 1528 # |||| / delay
1691 # cmd pid ||||| time | caller 1529 # cmd pid ||||| time | caller
1692 # \ / ||||| \ | / 1530 # \ / ||||| \ | /
1693 sshd-1991 1d.h. 0us+: irq_enter < 1531 sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ
1694 sshd-1991 1d..1 46us : irq_exit <- 1532 sshd-1991 1d..1 46us : irq_exit <-do_IRQ
1695 sshd-1991 1d..1 47us+: trace_preem 1533 sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ
1696 sshd-1991 1d..1 52us : <stack trac 1534 sshd-1991 1d..1 52us : <stack trace>
1697 => sub_preempt_count 1535 => sub_preempt_count
1698 => irq_exit 1536 => irq_exit
1699 => do_IRQ 1537 => do_IRQ
1700 => ret_from_intr 1538 => ret_from_intr
1701 1539
1702 1540
1703 This has some more changes. Preemption was di 1541 This has some more changes. Preemption was disabled when an
1704 interrupt came in (notice the 'h'), and was e 1542 interrupt came in (notice the 'h'), and was enabled on exit.
1705 But we also see that interrupts have been dis 1543 But we also see that interrupts have been disabled when entering
1706 the preempt off section and leaving it (the ' 1544 the preempt off section and leaving it (the 'd'). We do not know if
1707 interrupts were enabled in the mean time or s 1545 interrupts were enabled in the mean time or shortly after this
1708 was over. 1546 was over.
1709 :: 1547 ::
1710 1548
1711 # tracer: preemptoff 1549 # tracer: preemptoff
1712 # 1550 #
1713 # preemptoff latency trace v1.1.5 on 3.8.0- 1551 # preemptoff latency trace v1.1.5 on 3.8.0-test+
1714 # ----------------------------------------- 1552 # --------------------------------------------------------------------
1715 # latency: 83 us, #241/241, CPU#1 | (M:pree 1553 # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1716 # ----------------- 1554 # -----------------
1717 # | task: bash-1994 (uid:0 nice:0 policy 1555 # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
1718 # ----------------- 1556 # -----------------
1719 # => started at: wake_up_new_task 1557 # => started at: wake_up_new_task
1720 # => ended at: task_rq_unlock 1558 # => ended at: task_rq_unlock
1721 # 1559 #
1722 # 1560 #
1723 # _------=> CPU# 1561 # _------=> CPU#
1724 # / _-----=> irqs-off 1562 # / _-----=> irqs-off
1725 # | / _----=> need-resched 1563 # | / _----=> need-resched
1726 # || / _---=> hardirq/softir 1564 # || / _---=> hardirq/softirq
1727 # ||| / _--=> preempt-depth 1565 # ||| / _--=> preempt-depth
1728 # |||| / delay 1566 # |||| / delay
1729 # cmd pid ||||| time | caller 1567 # cmd pid ||||| time | caller
1730 # \ / ||||| \ | / 1568 # \ / ||||| \ | /
1731 bash-1994 1d..1 0us : _raw_spin_l 1569 bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task
1732 bash-1994 1d..1 0us : select_task 1570 bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq
1733 bash-1994 1d..1 1us : __rcu_read_ 1571 bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair
1734 bash-1994 1d..1 1us : source_load 1572 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
1735 bash-1994 1d..1 1us : source_load 1573 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
1736 [...] 1574 [...]
1737 bash-1994 1d..1 12us : irq_enter < 1575 bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt
1738 bash-1994 1d..1 12us : rcu_irq_ent 1576 bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter
1739 bash-1994 1d..1 13us : add_preempt 1577 bash-1994 1d..1 13us : add_preempt_count <-irq_enter
1740 bash-1994 1d.h1 13us : exit_idle < 1578 bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt
1741 bash-1994 1d.h1 13us : hrtimer_int 1579 bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt
1742 bash-1994 1d.h1 13us : _raw_spin_l 1580 bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt
1743 bash-1994 1d.h1 14us : add_preempt 1581 bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock
1744 bash-1994 1d.h2 14us : ktime_get_u 1582 bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt
1745 [...] 1583 [...]
1746 bash-1994 1d.h1 35us : lapic_next_ 1584 bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event
1747 bash-1994 1d.h1 35us : irq_exit <- 1585 bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt
1748 bash-1994 1d.h1 36us : sub_preempt 1586 bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit
1749 bash-1994 1d..2 36us : do_softirq 1587 bash-1994 1d..2 36us : do_softirq <-irq_exit
1750 bash-1994 1d..2 36us : __do_softir 1588 bash-1994 1d..2 36us : __do_softirq <-call_softirq
1751 bash-1994 1d..2 36us : __local_bh_ 1589 bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq
1752 bash-1994 1d.s2 37us : add_preempt 1590 bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq
1753 bash-1994 1d.s3 38us : _raw_spin_u 1591 bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq
1754 bash-1994 1d.s3 39us : sub_preempt 1592 bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock
1755 bash-1994 1d.s2 39us : call_timer_ 1593 bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq
1756 [...] 1594 [...]
1757 bash-1994 1dNs2 81us : cpu_needs_a 1595 bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks
1758 bash-1994 1dNs2 82us : __local_bh_ 1596 bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq
1759 bash-1994 1dNs2 82us : sub_preempt 1597 bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable
1760 bash-1994 1dN.2 82us : idle_cpu <- 1598 bash-1994 1dN.2 82us : idle_cpu <-irq_exit
1761 bash-1994 1dN.2 83us : rcu_irq_exi 1599 bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit
1762 bash-1994 1dN.2 83us : sub_preempt 1600 bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit
1763 bash-1994 1.N.1 84us : _raw_spin_u 1601 bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
1764 bash-1994 1.N.1 84us+: trace_preem 1602 bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock
1765 bash-1994 1.N.1 104us : <stack trac 1603 bash-1994 1.N.1 104us : <stack trace>
1766 => sub_preempt_count 1604 => sub_preempt_count
1767 => _raw_spin_unlock_irqrestore 1605 => _raw_spin_unlock_irqrestore
1768 => task_rq_unlock 1606 => task_rq_unlock
1769 => wake_up_new_task 1607 => wake_up_new_task
1770 => do_fork 1608 => do_fork
1771 => sys_clone 1609 => sys_clone
1772 => stub_clone 1610 => stub_clone
1773 1611
1774 1612
1775 The above is an example of the preemptoff tra 1613 The above is an example of the preemptoff trace with
1776 function-trace set. Here we see that interrup 1614 function-trace set. Here we see that interrupts were not disabled
1777 the entire time. The irq_enter code lets us k 1615 the entire time. The irq_enter code lets us know that we entered
1778 an interrupt 'h'. Before that, the functions 1616 an interrupt 'h'. Before that, the functions being traced still
1779 show that it is not in an interrupt, but we c 1617 show that it is not in an interrupt, but we can see from the
1780 functions themselves that this is not the cas 1618 functions themselves that this is not the case.
1781 1619
1782 preemptirqsoff 1620 preemptirqsoff
1783 -------------- 1621 --------------
1784 1622
1785 Knowing the locations that have interrupts di 1623 Knowing the locations that have interrupts disabled or
1786 preemption disabled for the longest times is 1624 preemption disabled for the longest times is helpful. But
1787 sometimes we would like to know when either p 1625 sometimes we would like to know when either preemption and/or
1788 interrupts are disabled. 1626 interrupts are disabled.
1789 1627
1790 Consider the following code:: 1628 Consider the following code::
1791 1629
1792 local_irq_disable(); 1630 local_irq_disable();
1793 call_function_with_irqs_off(); 1631 call_function_with_irqs_off();
1794 preempt_disable(); 1632 preempt_disable();
1795 call_function_with_irqs_and_preemption_of 1633 call_function_with_irqs_and_preemption_off();
1796 local_irq_enable(); 1634 local_irq_enable();
1797 call_function_with_preemption_off(); 1635 call_function_with_preemption_off();
1798 preempt_enable(); 1636 preempt_enable();
1799 1637
1800 The irqsoff tracer will record the total leng 1638 The irqsoff tracer will record the total length of
1801 call_function_with_irqs_off() and 1639 call_function_with_irqs_off() and
1802 call_function_with_irqs_and_preemption_off(). 1640 call_function_with_irqs_and_preemption_off().
1803 1641
1804 The preemptoff tracer will record the total l 1642 The preemptoff tracer will record the total length of
1805 call_function_with_irqs_and_preemption_off() 1643 call_function_with_irqs_and_preemption_off() and
1806 call_function_with_preemption_off(). 1644 call_function_with_preemption_off().
1807 1645
1808 But neither will trace the time that interrup 1646 But neither will trace the time that interrupts and/or
1809 preemption is disabled. This total time is th 1647 preemption is disabled. This total time is the time that we can
1810 not schedule. To record this time, use the pr 1648 not schedule. To record this time, use the preemptirqsoff
1811 tracer. 1649 tracer.
1812 1650
1813 Again, using this trace is much like the irqs 1651 Again, using this trace is much like the irqsoff and preemptoff
1814 tracers. 1652 tracers.
1815 :: 1653 ::
1816 1654
1817 # echo 0 > options/function-trace 1655 # echo 0 > options/function-trace
1818 # echo preemptirqsoff > current_tracer 1656 # echo preemptirqsoff > current_tracer
1819 # echo 1 > tracing_on 1657 # echo 1 > tracing_on
1820 # echo 0 > tracing_max_latency 1658 # echo 0 > tracing_max_latency
1821 # ls -ltr 1659 # ls -ltr
1822 [...] 1660 [...]
1823 # echo 0 > tracing_on 1661 # echo 0 > tracing_on
1824 # cat trace 1662 # cat trace
1825 # tracer: preemptirqsoff 1663 # tracer: preemptirqsoff
1826 # 1664 #
1827 # preemptirqsoff latency trace v1.1.5 on 3. 1665 # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1828 # ----------------------------------------- 1666 # --------------------------------------------------------------------
1829 # latency: 100 us, #4/4, CPU#3 | (M:preempt 1667 # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1830 # ----------------- 1668 # -----------------
1831 # | task: ls-2230 (uid:0 nice:0 policy:0 1669 # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
1832 # ----------------- 1670 # -----------------
1833 # => started at: ata_scsi_queuecmd 1671 # => started at: ata_scsi_queuecmd
1834 # => ended at: ata_scsi_queuecmd 1672 # => ended at: ata_scsi_queuecmd
1835 # 1673 #
1836 # 1674 #
1837 # _------=> CPU# 1675 # _------=> CPU#
1838 # / _-----=> irqs-off 1676 # / _-----=> irqs-off
1839 # | / _----=> need-resched 1677 # | / _----=> need-resched
1840 # || / _---=> hardirq/softir 1678 # || / _---=> hardirq/softirq
1841 # ||| / _--=> preempt-depth 1679 # ||| / _--=> preempt-depth
1842 # |||| / delay 1680 # |||| / delay
1843 # cmd pid ||||| time | caller 1681 # cmd pid ||||| time | caller
1844 # \ / ||||| \ | / 1682 # \ / ||||| \ | /
1845 ls-2230 3d... 0us+: _raw_spin_l 1683 ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
1846 ls-2230 3...1 100us : _raw_spin_u 1684 ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1847 ls-2230 3...1 101us+: trace_preem 1685 ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd
1848 ls-2230 3...1 111us : <stack trac 1686 ls-2230 3...1 111us : <stack trace>
1849 => sub_preempt_count 1687 => sub_preempt_count
1850 => _raw_spin_unlock_irqrestore 1688 => _raw_spin_unlock_irqrestore
1851 => ata_scsi_queuecmd 1689 => ata_scsi_queuecmd
1852 => scsi_dispatch_cmd 1690 => scsi_dispatch_cmd
1853 => scsi_request_fn 1691 => scsi_request_fn
1854 => __blk_run_queue_uncond 1692 => __blk_run_queue_uncond
1855 => __blk_run_queue 1693 => __blk_run_queue
1856 => blk_queue_bio 1694 => blk_queue_bio
1857 => submit_bio_noacct !! 1695 => generic_make_request
1858 => submit_bio 1696 => submit_bio
1859 => submit_bh 1697 => submit_bh
1860 => ext3_bread 1698 => ext3_bread
1861 => ext3_dir_bread 1699 => ext3_dir_bread
1862 => htree_dirblock_to_tree 1700 => htree_dirblock_to_tree
1863 => ext3_htree_fill_tree 1701 => ext3_htree_fill_tree
1864 => ext3_readdir 1702 => ext3_readdir
1865 => vfs_readdir 1703 => vfs_readdir
1866 => sys_getdents 1704 => sys_getdents
1867 => system_call_fastpath 1705 => system_call_fastpath
1868 1706
1869 1707
1870 The trace_hardirqs_off_thunk is called from a 1708 The trace_hardirqs_off_thunk is called from assembly on x86 when
1871 interrupts are disabled in the assembly code. 1709 interrupts are disabled in the assembly code. Without the
1872 function tracing, we do not know if interrupt 1710 function tracing, we do not know if interrupts were enabled
1873 within the preemption points. We do see that 1711 within the preemption points. We do see that it started with
1874 preemption enabled. 1712 preemption enabled.
1875 1713
1876 Here is a trace with function-trace set:: 1714 Here is a trace with function-trace set::
1877 1715
1878 # tracer: preemptirqsoff 1716 # tracer: preemptirqsoff
1879 # 1717 #
1880 # preemptirqsoff latency trace v1.1.5 on 3. 1718 # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1881 # ----------------------------------------- 1719 # --------------------------------------------------------------------
1882 # latency: 161 us, #339/339, CPU#3 | (M:pre 1720 # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1883 # ----------------- 1721 # -----------------
1884 # | task: ls-2269 (uid:0 nice:0 policy:0 1722 # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
1885 # ----------------- 1723 # -----------------
1886 # => started at: schedule 1724 # => started at: schedule
1887 # => ended at: mutex_unlock 1725 # => ended at: mutex_unlock
1888 # 1726 #
1889 # 1727 #
1890 # _------=> CPU# 1728 # _------=> CPU#
1891 # / _-----=> irqs-off 1729 # / _-----=> irqs-off
1892 # | / _----=> need-resched 1730 # | / _----=> need-resched
1893 # || / _---=> hardirq/softir 1731 # || / _---=> hardirq/softirq
1894 # ||| / _--=> preempt-depth 1732 # ||| / _--=> preempt-depth
1895 # |||| / delay 1733 # |||| / delay
1896 # cmd pid ||||| time | caller 1734 # cmd pid ||||| time | caller
1897 # \ / ||||| \ | / 1735 # \ / ||||| \ | /
1898 kworker/-59 3...1 0us : __schedule 1736 kworker/-59 3...1 0us : __schedule <-schedule
1899 kworker/-59 3d..1 0us : rcu_preempt 1737 kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch
1900 kworker/-59 3d..1 1us : add_preempt 1738 kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq
1901 kworker/-59 3d..2 1us : deactivate_ 1739 kworker/-59 3d..2 1us : deactivate_task <-__schedule
1902 kworker/-59 3d..2 1us : dequeue_tas 1740 kworker/-59 3d..2 1us : dequeue_task <-deactivate_task
1903 kworker/-59 3d..2 2us : update_rq_c 1741 kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task
1904 kworker/-59 3d..2 2us : dequeue_tas 1742 kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task
1905 kworker/-59 3d..2 2us : update_curr 1743 kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair
1906 kworker/-59 3d..2 2us : update_min_ 1744 kworker/-59 3d..2 2us : update_min_vruntime <-update_curr
1907 kworker/-59 3d..2 3us : cpuacct_cha 1745 kworker/-59 3d..2 3us : cpuacct_charge <-update_curr
1908 kworker/-59 3d..2 3us : __rcu_read_ 1746 kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge
1909 kworker/-59 3d..2 3us : __rcu_read_ 1747 kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge
1910 kworker/-59 3d..2 3us : update_cfs_ 1748 kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair
1911 kworker/-59 3d..2 4us : clear_buddi 1749 kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair
1912 kworker/-59 3d..2 4us : account_ent 1750 kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair
1913 kworker/-59 3d..2 4us : update_min_ 1751 kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair
1914 kworker/-59 3d..2 4us : update_cfs_ 1752 kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair
1915 kworker/-59 3d..2 5us : hrtick_upda 1753 kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair
1916 kworker/-59 3d..2 5us : wq_worker_s 1754 kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule
1917 kworker/-59 3d..2 5us : kthread_dat 1755 kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping
1918 kworker/-59 3d..2 5us : put_prev_ta 1756 kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule
1919 kworker/-59 3d..2 6us : pick_next_t 1757 kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task
1920 kworker/-59 3d..2 6us : clear_buddi 1758 kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair
1921 kworker/-59 3d..2 6us : set_next_en 1759 kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair
1922 kworker/-59 3d..2 6us : update_stat 1760 kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity
1923 ls-2269 3d..2 7us : finish_task 1761 ls-2269 3d..2 7us : finish_task_switch <-__schedule
1924 ls-2269 3d..2 7us : _raw_spin_u 1762 ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch
1925 ls-2269 3d..2 8us : do_IRQ <-re 1763 ls-2269 3d..2 8us : do_IRQ <-ret_from_intr
1926 ls-2269 3d..2 8us : irq_enter < 1764 ls-2269 3d..2 8us : irq_enter <-do_IRQ
1927 ls-2269 3d..2 8us : rcu_irq_ent 1765 ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter
1928 ls-2269 3d..2 9us : add_preempt 1766 ls-2269 3d..2 9us : add_preempt_count <-irq_enter
1929 ls-2269 3d.h2 9us : exit_idle < 1767 ls-2269 3d.h2 9us : exit_idle <-do_IRQ
1930 [...] 1768 [...]
1931 ls-2269 3d.h3 20us : sub_preempt 1769 ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock
1932 ls-2269 3d.h2 20us : irq_exit <- 1770 ls-2269 3d.h2 20us : irq_exit <-do_IRQ
1933 ls-2269 3d.h2 21us : sub_preempt 1771 ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit
1934 ls-2269 3d..3 21us : do_softirq 1772 ls-2269 3d..3 21us : do_softirq <-irq_exit
1935 ls-2269 3d..3 21us : __do_softir 1773 ls-2269 3d..3 21us : __do_softirq <-call_softirq
1936 ls-2269 3d..3 21us+: __local_bh_ 1774 ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq
1937 ls-2269 3d.s4 29us : sub_preempt 1775 ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip
1938 ls-2269 3d.s5 29us : sub_preempt 1776 ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip
1939 ls-2269 3d.s5 31us : do_IRQ <-re 1777 ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr
1940 ls-2269 3d.s5 31us : irq_enter < 1778 ls-2269 3d.s5 31us : irq_enter <-do_IRQ
1941 ls-2269 3d.s5 31us : rcu_irq_ent 1779 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1942 [...] 1780 [...]
1943 ls-2269 3d.s5 31us : rcu_irq_ent 1781 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1944 ls-2269 3d.s5 32us : add_preempt 1782 ls-2269 3d.s5 32us : add_preempt_count <-irq_enter
1945 ls-2269 3d.H5 32us : exit_idle < 1783 ls-2269 3d.H5 32us : exit_idle <-do_IRQ
1946 ls-2269 3d.H5 32us : handle_irq 1784 ls-2269 3d.H5 32us : handle_irq <-do_IRQ
1947 ls-2269 3d.H5 32us : irq_to_desc 1785 ls-2269 3d.H5 32us : irq_to_desc <-handle_irq
1948 ls-2269 3d.H5 33us : handle_fast 1786 ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq
1949 [...] 1787 [...]
1950 ls-2269 3d.s5 158us : _raw_spin_u 1788 ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
1951 ls-2269 3d.s3 158us : net_rps_act 1789 ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
1952 ls-2269 3d.s3 159us : __local_bh_ 1790 ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq
1953 ls-2269 3d.s3 159us : sub_preempt 1791 ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable
1954 ls-2269 3d..3 159us : idle_cpu <- 1792 ls-2269 3d..3 159us : idle_cpu <-irq_exit
1955 ls-2269 3d..3 159us : rcu_irq_exi 1793 ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit
1956 ls-2269 3d..3 160us : sub_preempt 1794 ls-2269 3d..3 160us : sub_preempt_count <-irq_exit
1957 ls-2269 3d... 161us : __mutex_unl 1795 ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock
1958 ls-2269 3d... 162us+: trace_hardi 1796 ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock
1959 ls-2269 3d... 186us : <stack trac 1797 ls-2269 3d... 186us : <stack trace>
1960 => __mutex_unlock_slowpath 1798 => __mutex_unlock_slowpath
1961 => mutex_unlock 1799 => mutex_unlock
1962 => process_output 1800 => process_output
1963 => n_tty_write 1801 => n_tty_write
1964 => tty_write 1802 => tty_write
1965 => vfs_write 1803 => vfs_write
1966 => sys_write 1804 => sys_write
1967 => system_call_fastpath 1805 => system_call_fastpath
1968 1806
1969 This is an interesting trace. It started with 1807 This is an interesting trace. It started with kworker running and
1970 scheduling out and ls taking over. But as soo 1808 scheduling out and ls taking over. But as soon as ls released the
1971 rq lock and enabled interrupts (but not preem 1809 rq lock and enabled interrupts (but not preemption) an interrupt
1972 triggered. When the interrupt finished, it st 1810 triggered. When the interrupt finished, it started running softirqs.
1973 But while the softirq was running, another in 1811 But while the softirq was running, another interrupt triggered.
1974 When an interrupt is running inside a softirq 1812 When an interrupt is running inside a softirq, the annotation is 'H'.
1975 1813
1976 1814
1977 wakeup 1815 wakeup
1978 ------ 1816 ------
1979 1817
1980 One common case that people are interested in 1818 One common case that people are interested in tracing is the
1981 time it takes for a task that is woken to act 1819 time it takes for a task that is woken to actually wake up.
1982 Now for non Real-Time tasks, this can be arbi 1820 Now for non Real-Time tasks, this can be arbitrary. But tracing
1983 it nonetheless can be interesting. !! 1821 it none the less can be interesting.
1984 1822
1985 Without function tracing:: 1823 Without function tracing::
1986 1824
1987 # echo 0 > options/function-trace 1825 # echo 0 > options/function-trace
1988 # echo wakeup > current_tracer 1826 # echo wakeup > current_tracer
1989 # echo 1 > tracing_on 1827 # echo 1 > tracing_on
1990 # echo 0 > tracing_max_latency 1828 # echo 0 > tracing_max_latency
1991 # chrt -f 5 sleep 1 1829 # chrt -f 5 sleep 1
1992 # echo 0 > tracing_on 1830 # echo 0 > tracing_on
1993 # cat trace 1831 # cat trace
1994 # tracer: wakeup 1832 # tracer: wakeup
1995 # 1833 #
1996 # wakeup latency trace v1.1.5 on 3.8.0-test 1834 # wakeup latency trace v1.1.5 on 3.8.0-test+
1997 # ----------------------------------------- 1835 # --------------------------------------------------------------------
1998 # latency: 15 us, #4/4, CPU#3 | (M:preempt 1836 # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1999 # ----------------- 1837 # -----------------
2000 # | task: kworker/3:1H-312 (uid:0 nice:- 1838 # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
2001 # ----------------- 1839 # -----------------
2002 # 1840 #
2003 # _------=> CPU# 1841 # _------=> CPU#
2004 # / _-----=> irqs-off 1842 # / _-----=> irqs-off
2005 # | / _----=> need-resched 1843 # | / _----=> need-resched
2006 # || / _---=> hardirq/softir 1844 # || / _---=> hardirq/softirq
2007 # ||| / _--=> preempt-depth 1845 # ||| / _--=> preempt-depth
2008 # |||| / delay 1846 # |||| / delay
2009 # cmd pid ||||| time | caller 1847 # cmd pid ||||| time | caller
2010 # \ / ||||| \ | / 1848 # \ / ||||| \ | /
2011 <idle>-0 3dNs7 0us : 0:120: 1849 <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H
2012 <idle>-0 3dNs7 1us+: ttwu_do_act 1850 <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
2013 <idle>-0 3d..3 15us : __schedule 1851 <idle>-0 3d..3 15us : __schedule <-schedule
2014 <idle>-0 3d..3 15us : 0:120: 1852 <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H
2015 1853
2016 The tracer only traces the highest priority t 1854 The tracer only traces the highest priority task in the system
2017 to avoid tracing the normal circumstances. He 1855 to avoid tracing the normal circumstances. Here we see that
2018 the kworker with a nice priority of -20 (not 1856 the kworker with a nice priority of -20 (not very nice), took
2019 just 15 microseconds from the time it woke up 1857 just 15 microseconds from the time it woke up, to the time it
2020 ran. 1858 ran.
2021 1859
2022 Non Real-Time tasks are not that interesting. 1860 Non Real-Time tasks are not that interesting. A more interesting
2023 trace is to concentrate only on Real-Time tas 1861 trace is to concentrate only on Real-Time tasks.
2024 1862
2025 wakeup_rt 1863 wakeup_rt
2026 --------- 1864 ---------
2027 1865
2028 In a Real-Time environment it is very importa 1866 In a Real-Time environment it is very important to know the
2029 wakeup time it takes for the highest priority 1867 wakeup time it takes for the highest priority task that is woken
2030 up to the time that it executes. This is also 1868 up to the time that it executes. This is also known as "schedule
2031 latency". I stress the point that this is abo 1869 latency". I stress the point that this is about RT tasks. It is
2032 also important to know the scheduling latency 1870 also important to know the scheduling latency of non-RT tasks,
2033 but the average schedule latency is better fo 1871 but the average schedule latency is better for non-RT tasks.
2034 Tools like LatencyTop are more appropriate fo 1872 Tools like LatencyTop are more appropriate for such
2035 measurements. 1873 measurements.
2036 1874
2037 Real-Time environments are interested in the 1875 Real-Time environments are interested in the worst case latency.
2038 That is the longest latency it takes for some 1876 That is the longest latency it takes for something to happen,
2039 and not the average. We can have a very fast 1877 and not the average. We can have a very fast scheduler that may
2040 only have a large latency once in a while, bu 1878 only have a large latency once in a while, but that would not
2041 work well with Real-Time tasks. The wakeup_r 1879 work well with Real-Time tasks. The wakeup_rt tracer was designed
2042 to record the worst case wakeups of RT tasks. 1880 to record the worst case wakeups of RT tasks. Non-RT tasks are
2043 not recorded because the tracer only records 1881 not recorded because the tracer only records one worst case and
2044 tracing non-RT tasks that are unpredictable w 1882 tracing non-RT tasks that are unpredictable will overwrite the
2045 worst case latency of RT tasks (just run the 1883 worst case latency of RT tasks (just run the normal wakeup
2046 tracer for a while to see that effect). 1884 tracer for a while to see that effect).
2047 1885
2048 Since this tracer only deals with RT tasks, w 1886 Since this tracer only deals with RT tasks, we will run this
2049 slightly differently than we did with the pre 1887 slightly differently than we did with the previous tracers.
2050 Instead of performing an 'ls', we will run 's 1888 Instead of performing an 'ls', we will run 'sleep 1' under
2051 'chrt' which changes the priority of the task 1889 'chrt' which changes the priority of the task.
2052 :: 1890 ::
2053 1891
2054 # echo 0 > options/function-trace 1892 # echo 0 > options/function-trace
2055 # echo wakeup_rt > current_tracer 1893 # echo wakeup_rt > current_tracer
2056 # echo 1 > tracing_on 1894 # echo 1 > tracing_on
2057 # echo 0 > tracing_max_latency 1895 # echo 0 > tracing_max_latency
2058 # chrt -f 5 sleep 1 1896 # chrt -f 5 sleep 1
2059 # echo 0 > tracing_on 1897 # echo 0 > tracing_on
2060 # cat trace 1898 # cat trace
2061 # tracer: wakeup 1899 # tracer: wakeup
2062 # 1900 #
2063 # tracer: wakeup_rt 1901 # tracer: wakeup_rt
2064 # 1902 #
2065 # wakeup_rt latency trace v1.1.5 on 3.8.0-t 1903 # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
2066 # ----------------------------------------- 1904 # --------------------------------------------------------------------
2067 # latency: 5 us, #4/4, CPU#3 | (M:preempt V 1905 # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
2068 # ----------------- 1906 # -----------------
2069 # | task: sleep-2389 (uid:0 nice:0 polic 1907 # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
2070 # ----------------- 1908 # -----------------
2071 # 1909 #
2072 # _------=> CPU# 1910 # _------=> CPU#
2073 # / _-----=> irqs-off 1911 # / _-----=> irqs-off
2074 # | / _----=> need-resched 1912 # | / _----=> need-resched
2075 # || / _---=> hardirq/softir 1913 # || / _---=> hardirq/softirq
2076 # ||| / _--=> preempt-depth 1914 # ||| / _--=> preempt-depth
2077 # |||| / delay 1915 # |||| / delay
2078 # cmd pid ||||| time | caller 1916 # cmd pid ||||| time | caller
2079 # \ / ||||| \ | / 1917 # \ / ||||| \ | /
2080 <idle>-0 3d.h4 0us : 0:120: 1918 <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep
2081 <idle>-0 3d.h4 1us+: ttwu_do_act 1919 <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
2082 <idle>-0 3d..3 5us : __schedule 1920 <idle>-0 3d..3 5us : __schedule <-schedule
2083 <idle>-0 3d..3 5us : 0:120: 1921 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
2084 1922
2085 1923
2086 Running this on an idle system, we see that i 1924 Running this on an idle system, we see that it only took 5 microseconds
2087 to perform the task switch. Note, since the 1925 to perform the task switch. Note, since the trace point in the schedule
2088 is before the actual "switch", we stop the tr 1926 is before the actual "switch", we stop the tracing when the recorded task
2089 is about to schedule in. This may change if w 1927 is about to schedule in. This may change if we add a new marker at the
2090 end of the scheduler. 1928 end of the scheduler.
2091 1929
2092 Notice that the recorded task is 'sleep' with 1930 Notice that the recorded task is 'sleep' with the PID of 2389
2093 and it has an rt_prio of 5. This priority is 1931 and it has an rt_prio of 5. This priority is user-space priority
2094 and not the internal kernel priority. The pol 1932 and not the internal kernel priority. The policy is 1 for
2095 SCHED_FIFO and 2 for SCHED_RR. 1933 SCHED_FIFO and 2 for SCHED_RR.
2096 1934
2097 Note, that the trace data shows the internal 1935 Note, that the trace data shows the internal priority (99 - rtprio).
2098 :: 1936 ::
2099 1937
2100 <idle>-0 3d..3 5us : 0:120:R 1938 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
2101 1939
2102 The 0:120:R means idle was running with a nic 1940 The 0:120:R means idle was running with a nice priority of 0 (120 - 120)
2103 and in the running state 'R'. The sleep task 1941 and in the running state 'R'. The sleep task was scheduled in with
2104 2389: 94:R. That is the priority is the kerne 1942 2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
2105 and it too is in the running state. 1943 and it too is in the running state.
2106 1944
2107 Doing the same with chrt -r 5 and function-tr 1945 Doing the same with chrt -r 5 and function-trace set.
2108 :: 1946 ::
2109 1947
2110 echo 1 > options/function-trace 1948 echo 1 > options/function-trace
2111 1949
2112 # tracer: wakeup_rt 1950 # tracer: wakeup_rt
2113 # 1951 #
2114 # wakeup_rt latency trace v1.1.5 on 3.8.0-t 1952 # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
2115 # ----------------------------------------- 1953 # --------------------------------------------------------------------
2116 # latency: 29 us, #85/85, CPU#3 | (M:preemp 1954 # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
2117 # ----------------- 1955 # -----------------
2118 # | task: sleep-2448 (uid:0 nice:0 polic 1956 # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
2119 # ----------------- 1957 # -----------------
2120 # 1958 #
2121 # _------=> CPU# 1959 # _------=> CPU#
2122 # / _-----=> irqs-off 1960 # / _-----=> irqs-off
2123 # | / _----=> need-resched 1961 # | / _----=> need-resched
2124 # || / _---=> hardirq/softir 1962 # || / _---=> hardirq/softirq
2125 # ||| / _--=> preempt-depth 1963 # ||| / _--=> preempt-depth
2126 # |||| / delay 1964 # |||| / delay
2127 # cmd pid ||||| time | caller 1965 # cmd pid ||||| time | caller
2128 # \ / ||||| \ | / 1966 # \ / ||||| \ | /
2129 <idle>-0 3d.h4 1us+: 0:120: 1967 <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep
2130 <idle>-0 3d.h4 2us : ttwu_do_act 1968 <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
2131 <idle>-0 3d.h3 3us : check_preem 1969 <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup
2132 <idle>-0 3d.h3 3us : resched_cur 1970 <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr
2133 <idle>-0 3dNh3 4us : task_woken_ 1971 <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup
2134 <idle>-0 3dNh3 4us : _raw_spin_u 1972 <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up
2135 <idle>-0 3dNh3 4us : sub_preempt 1973 <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock
2136 <idle>-0 3dNh2 5us : ttwu_stat < 1974 <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up
2137 <idle>-0 3dNh2 5us : _raw_spin_u 1975 <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
2138 <idle>-0 3dNh2 6us : sub_preempt 1976 <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
2139 <idle>-0 3dNh1 6us : _raw_spin_l 1977 <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer
2140 <idle>-0 3dNh1 6us : add_preempt 1978 <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock
2141 <idle>-0 3dNh2 7us : _raw_spin_u 1979 <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt
2142 <idle>-0 3dNh2 7us : sub_preempt 1980 <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock
2143 <idle>-0 3dNh1 7us : tick_progra 1981 <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt
2144 <idle>-0 3dNh1 7us : clockevents 1982 <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event
2145 <idle>-0 3dNh1 8us : ktime_get < 1983 <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event
2146 <idle>-0 3dNh1 8us : lapic_next_ 1984 <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event
2147 <idle>-0 3dNh1 8us : irq_exit <- 1985 <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt
2148 <idle>-0 3dNh1 9us : sub_preempt 1986 <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit
2149 <idle>-0 3dN.2 9us : idle_cpu <- 1987 <idle>-0 3dN.2 9us : idle_cpu <-irq_exit
2150 <idle>-0 3dN.2 9us : rcu_irq_exi 1988 <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit
2151 <idle>-0 3dN.2 10us : rcu_eqs_ent 1989 <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
2152 <idle>-0 3dN.2 10us : sub_preempt 1990 <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit
2153 <idle>-0 3.N.1 11us : rcu_idle_ex 1991 <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle
2154 <idle>-0 3dN.1 11us : rcu_eqs_exi 1992 <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
2155 <idle>-0 3.N.1 11us : tick_nohz_i 1993 <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle
2156 <idle>-0 3dN.1 12us : menu_hrtime 1994 <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
2157 <idle>-0 3dN.1 12us : ktime_get < 1995 <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit
2158 <idle>-0 3dN.1 12us : tick_do_upd 1996 <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
2159 <idle>-0 3dN.1 13us : cpu_load_up 1997 <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit
2160 <idle>-0 3dN.1 13us : _raw_spin_l 1998 <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz
2161 <idle>-0 3dN.1 13us : add_preempt 1999 <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock
2162 <idle>-0 3dN.2 13us : __cpu_load_ 2000 <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz
2163 <idle>-0 3dN.2 14us : sched_avg_u 2001 <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update
2164 <idle>-0 3dN.2 14us : _raw_spin_u 2002 <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz
2165 <idle>-0 3dN.2 14us : sub_preempt 2003 <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock
2166 <idle>-0 3dN.1 15us : calc_load_n 2004 <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit
2167 <idle>-0 3dN.1 15us : touch_softl 2005 <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
2168 <idle>-0 3dN.1 15us : hrtimer_can 2006 <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit
2169 <idle>-0 3dN.1 15us : hrtimer_try 2007 <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel
2170 <idle>-0 3dN.1 16us : lock_hrtime 2008 <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
2171 <idle>-0 3dN.1 16us : _raw_spin_l 2009 <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
2172 <idle>-0 3dN.1 16us : add_preempt 2010 <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave
2173 <idle>-0 3dN.2 17us : __remove_hr 2011 <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16
2174 <idle>-0 3dN.2 17us : hrtimer_for 2012 <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer
2175 <idle>-0 3dN.2 17us : tick_progra 2013 <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram
2176 <idle>-0 3dN.2 18us : clockevents 2014 <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event
2177 <idle>-0 3dN.2 18us : ktime_get < 2015 <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event
2178 <idle>-0 3dN.2 18us : lapic_next_ 2016 <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event
2179 <idle>-0 3dN.2 19us : _raw_spin_u 2017 <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
2180 <idle>-0 3dN.2 19us : sub_preempt 2018 <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
2181 <idle>-0 3dN.1 19us : hrtimer_for 2019 <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit
2182 <idle>-0 3dN.1 20us : ktime_add_s 2020 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
2183 <idle>-0 3dN.1 20us : ktime_add_s 2021 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
2184 <idle>-0 3dN.1 20us : hrtimer_sta 2022 <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
2185 <idle>-0 3dN.1 20us : __hrtimer_s 2023 <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
2186 <idle>-0 3dN.1 21us : lock_hrtime 2024 <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
2187 <idle>-0 3dN.1 21us : _raw_spin_l 2025 <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
2188 <idle>-0 3dN.1 21us : add_preempt 2026 <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave
2189 <idle>-0 3dN.2 22us : ktime_add_s 2027 <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns
2190 <idle>-0 3dN.2 22us : enqueue_hrt 2028 <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns
2191 <idle>-0 3dN.2 22us : tick_progra 2029 <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns
2192 <idle>-0 3dN.2 23us : clockevents 2030 <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event
2193 <idle>-0 3dN.2 23us : ktime_get < 2031 <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event
2194 <idle>-0 3dN.2 23us : lapic_next_ 2032 <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event
2195 <idle>-0 3dN.2 24us : _raw_spin_u 2033 <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
2196 <idle>-0 3dN.2 24us : sub_preempt 2034 <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
2197 <idle>-0 3dN.1 24us : account_idl 2035 <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit
2198 <idle>-0 3dN.1 24us : account_idl 2036 <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks
2199 <idle>-0 3.N.1 25us : sub_preempt 2037 <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle
2200 <idle>-0 3.N.. 25us : schedule <- 2038 <idle>-0 3.N.. 25us : schedule <-cpu_idle
2201 <idle>-0 3.N.. 25us : __schedule 2039 <idle>-0 3.N.. 25us : __schedule <-preempt_schedule
2202 <idle>-0 3.N.. 26us : add_preempt 2040 <idle>-0 3.N.. 26us : add_preempt_count <-__schedule
2203 <idle>-0 3.N.1 26us : rcu_note_co 2041 <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule
2204 <idle>-0 3.N.1 26us : rcu_sched_q 2042 <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch
2205 <idle>-0 3dN.1 27us : rcu_preempt 2043 <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch
2206 <idle>-0 3.N.1 27us : _raw_spin_l 2044 <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule
2207 <idle>-0 3dN.1 27us : add_preempt 2045 <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq
2208 <idle>-0 3dN.2 28us : put_prev_ta 2046 <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule
2209 <idle>-0 3dN.2 28us : pick_next_t 2047 <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task
2210 <idle>-0 3dN.2 28us : pick_next_t 2048 <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task
2211 <idle>-0 3dN.2 29us : dequeue_pus 2049 <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt
2212 <idle>-0 3d..3 29us : __schedule 2050 <idle>-0 3d..3 29us : __schedule <-preempt_schedule
2213 <idle>-0 3d..3 30us : 0:120: 2051 <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep
2214 2052
2215 This isn't that big of a trace, even with fun 2053 This isn't that big of a trace, even with function tracing enabled,
2216 so I included the entire trace. 2054 so I included the entire trace.
2217 2055
2218 The interrupt went off while when the system 2056 The interrupt went off while when the system was idle. Somewhere
2219 before task_woken_rt() was called, the NEED_R 2057 before task_woken_rt() was called, the NEED_RESCHED flag was set,
2220 this is indicated by the first occurrence of 2058 this is indicated by the first occurrence of the 'N' flag.
2221 2059
2222 Latency tracing and events 2060 Latency tracing and events
2223 -------------------------- 2061 --------------------------
2224 As function tracing can induce a much larger 2062 As function tracing can induce a much larger latency, but without
2225 seeing what happens within the latency it is 2063 seeing what happens within the latency it is hard to know what
2226 caused it. There is a middle ground, and that 2064 caused it. There is a middle ground, and that is with enabling
2227 events. 2065 events.
2228 :: 2066 ::
2229 2067
2230 # echo 0 > options/function-trace 2068 # echo 0 > options/function-trace
2231 # echo wakeup_rt > current_tracer 2069 # echo wakeup_rt > current_tracer
2232 # echo 1 > events/enable 2070 # echo 1 > events/enable
2233 # echo 1 > tracing_on 2071 # echo 1 > tracing_on
2234 # echo 0 > tracing_max_latency 2072 # echo 0 > tracing_max_latency
2235 # chrt -f 5 sleep 1 2073 # chrt -f 5 sleep 1
2236 # echo 0 > tracing_on 2074 # echo 0 > tracing_on
2237 # cat trace 2075 # cat trace
2238 # tracer: wakeup_rt 2076 # tracer: wakeup_rt
2239 # 2077 #
2240 # wakeup_rt latency trace v1.1.5 on 3.8.0-t 2078 # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
2241 # ----------------------------------------- 2079 # --------------------------------------------------------------------
2242 # latency: 6 us, #12/12, CPU#2 | (M:preempt 2080 # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
2243 # ----------------- 2081 # -----------------
2244 # | task: sleep-5882 (uid:0 nice:0 polic 2082 # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
2245 # ----------------- 2083 # -----------------
2246 # 2084 #
2247 # _------=> CPU# 2085 # _------=> CPU#
2248 # / _-----=> irqs-off 2086 # / _-----=> irqs-off
2249 # | / _----=> need-resched 2087 # | / _----=> need-resched
2250 # || / _---=> hardirq/softir 2088 # || / _---=> hardirq/softirq
2251 # ||| / _--=> preempt-depth 2089 # ||| / _--=> preempt-depth
2252 # |||| / delay 2090 # |||| / delay
2253 # cmd pid ||||| time | caller 2091 # cmd pid ||||| time | caller
2254 # \ / ||||| \ | / 2092 # \ / ||||| \ | /
2255 <idle>-0 2d.h4 0us : 0:120: 2093 <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep
2256 <idle>-0 2d.h4 0us : ttwu_do_act 2094 <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
2257 <idle>-0 2d.h4 1us : sched_wakeu 2095 <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
2258 <idle>-0 2dNh2 1us : hrtimer_exp 2096 <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
2259 <idle>-0 2.N.2 2us : power_end: 2097 <idle>-0 2.N.2 2us : power_end: cpu_id=2
2260 <idle>-0 2.N.2 3us : cpu_idle: s 2098 <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2
2261 <idle>-0 2dN.3 4us : hrtimer_can 2099 <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
2262 <idle>-0 2dN.3 4us : hrtimer_sta 2100 <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
2263 <idle>-0 2.N.2 5us : rcu_utiliza 2101 <idle>-0 2.N.2 5us : rcu_utilization: Start context switch
2264 <idle>-0 2.N.2 5us : rcu_utiliza 2102 <idle>-0 2.N.2 5us : rcu_utilization: End context switch
2265 <idle>-0 2d..3 6us : __schedule 2103 <idle>-0 2d..3 6us : __schedule <-schedule
2266 <idle>-0 2d..3 6us : 0:120: 2104 <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep
2267 2105
2268 2106
2269 Hardware Latency Detector 2107 Hardware Latency Detector
2270 ------------------------- 2108 -------------------------
2271 2109
2272 The hardware latency detector is executed by 2110 The hardware latency detector is executed by enabling the "hwlat" tracer.
2273 2111
2274 NOTE, this tracer will affect the performance 2112 NOTE, this tracer will affect the performance of the system as it will
2275 periodically make a CPU constantly busy with 2113 periodically make a CPU constantly busy with interrupts disabled.
2276 :: 2114 ::
2277 2115
2278 # echo hwlat > current_tracer 2116 # echo hwlat > current_tracer
2279 # sleep 100 2117 # sleep 100
2280 # cat trace 2118 # cat trace
2281 # tracer: hwlat 2119 # tracer: hwlat
2282 # 2120 #
2283 # entries-in-buffer/entries-written: 13/13 <<
2284 # <<
2285 # _-----=> irq 2121 # _-----=> irqs-off
2286 # / _----=> nee 2122 # / _----=> need-resched
2287 # | / _---=> har 2123 # | / _---=> hardirq/softirq
2288 # || / _--=> pre 2124 # || / _--=> preempt-depth
2289 # ||| / dela 2125 # ||| / delay
2290 # TASK-PID CPU# |||| TIMEST 2126 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
2291 # | | | |||| | 2127 # | | | |||| | |
2292 <...>-1729 [001] d... 678.473 !! 2128 <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940
2293 <...>-1729 [004] d... 689.556 !! 2129 <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365
2294 <...>-1729 [005] d... 714.756 !! 2130 <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062
2295 <...>-1729 [001] d... 718.788 !! 2131 <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633
2296 <...>-1729 [002] d... 719.796 !! 2132 <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961
2297 <...>-1729 [006] d... 844.787 !! 2133 <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1
2298 <...>-1729 [003] d... 849.827 <<
2299 <...>-1729 [007] d... 853.859 <<
2300 <...>-1729 [001] d... 855.874 <<
2301 <...>-1729 [001] d... 863.938 <<
2302 <...>-1729 [007] d... 878.050 <<
2303 <...>-1729 [007] d... 886.114 <<
2304 2134
2305 2135
2306 The above output is somewhat the same in the 2136 The above output is somewhat the same in the header. All events will have
2307 interrupts disabled 'd'. Under the FUNCTION t 2137 interrupts disabled 'd'. Under the FUNCTION title there is:
2308 2138
2309 #1 2139 #1
2310 This is the count of events recorded 2140 This is the count of events recorded that were greater than the
2311 tracing_threshold (See below). 2141 tracing_threshold (See below).
2312 2142
2313 inner/outer(us): 11/11 !! 2143 inner/outer(us): 12/14
2314 2144
2315 This shows two numbers as "inner latenc 2145 This shows two numbers as "inner latency" and "outer latency". The test
2316 runs in a loop checking a timestamp twi 2146 runs in a loop checking a timestamp twice. The latency detected within
2317 the two timestamps is the "inner latenc 2147 the two timestamps is the "inner latency" and the latency detected
2318 after the previous timestamp and the ne 2148 after the previous timestamp and the next timestamp in the loop is
2319 the "outer latency". 2149 the "outer latency".
2320 2150
2321 ts:1581527483.343962693 !! 2151 ts:1499801089.066141940
2322 2152
2323 The absolute timestamp that the first l !! 2153 The absolute timestamp that the event happened.
2324 2154
2325 count:6 !! 2155 nmi-total:4 nmi-count:1
2326 <<
2327 The number of times a latency was detec <<
2328 <<
2329 nmi-total:7 nmi-count:1 <<
2330 2156
2331 On architectures that support it, if an 2157 On architectures that support it, if an NMI comes in during the
2332 test, the time spent in NMI is reported 2158 test, the time spent in NMI is reported in "nmi-total" (in
2333 microseconds). 2159 microseconds).
2334 2160
2335 All architectures that have NMIs will s 2161 All architectures that have NMIs will show the "nmi-count" if an
2336 NMI comes in during the test. 2162 NMI comes in during the test.
2337 2163
2338 hwlat files: 2164 hwlat files:
2339 2165
2340 tracing_threshold 2166 tracing_threshold
2341 This gets automatically set to "10" t 2167 This gets automatically set to "10" to represent 10
2342 microseconds. This is the threshold o 2168 microseconds. This is the threshold of latency that
2343 needs to be detected before the trace 2169 needs to be detected before the trace will be recorded.
2344 2170
2345 Note, when hwlat tracer is finished ( 2171 Note, when hwlat tracer is finished (another tracer is
2346 written into "current_tracer"), the o 2172 written into "current_tracer"), the original value for
2347 tracing_threshold is placed back into 2173 tracing_threshold is placed back into this file.
2348 2174
2349 hwlat_detector/width 2175 hwlat_detector/width
2350 The length of time the test runs with 2176 The length of time the test runs with interrupts disabled.
2351 2177
2352 hwlat_detector/window 2178 hwlat_detector/window
2353 The length of time of the window whic 2179 The length of time of the window which the test
2354 runs. That is, the test will run for 2180 runs. That is, the test will run for "width"
2355 microseconds per "window" microsecond 2181 microseconds per "window" microseconds
2356 2182
2357 tracing_cpumask 2183 tracing_cpumask
2358 When the test is started. A kernel th 2184 When the test is started. A kernel thread is created that
2359 runs the test. This thread will alter 2185 runs the test. This thread will alternate between CPUs
2360 listed in the tracing_cpumask between 2186 listed in the tracing_cpumask between each period
2361 (one "window"). To limit the test to 2187 (one "window"). To limit the test to specific CPUs
2362 set the mask in this file to only the 2188 set the mask in this file to only the CPUs that the test
2363 should run on. 2189 should run on.
2364 2190
2365 function 2191 function
2366 -------- 2192 --------
2367 2193
2368 This tracer is the function tracer. Enabling 2194 This tracer is the function tracer. Enabling the function tracer
2369 can be done from the debug file system. Make 2195 can be done from the debug file system. Make sure the
2370 ftrace_enabled is set; otherwise this tracer 2196 ftrace_enabled is set; otherwise this tracer is a nop.
2371 See the "ftrace_enabled" section below. 2197 See the "ftrace_enabled" section below.
2372 :: 2198 ::
2373 2199
2374 # sysctl kernel.ftrace_enabled=1 2200 # sysctl kernel.ftrace_enabled=1
2375 # echo function > current_tracer 2201 # echo function > current_tracer
2376 # echo 1 > tracing_on 2202 # echo 1 > tracing_on
2377 # usleep 1 2203 # usleep 1
2378 # echo 0 > tracing_on 2204 # echo 0 > tracing_on
2379 # cat trace 2205 # cat trace
2380 # tracer: function 2206 # tracer: function
2381 # 2207 #
2382 # entries-in-buffer/entries-written: 24799/ 2208 # entries-in-buffer/entries-written: 24799/24799 #P:4
2383 # 2209 #
2384 # _-----=> irq 2210 # _-----=> irqs-off
2385 # / _----=> nee 2211 # / _----=> need-resched
2386 # | / _---=> har 2212 # | / _---=> hardirq/softirq
2387 # || / _--=> pre 2213 # || / _--=> preempt-depth
2388 # ||| / dela 2214 # ||| / delay
2389 # TASK-PID CPU# |||| TIMEST 2215 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
2390 # | | | |||| | 2216 # | | | |||| | |
2391 bash-1994 [002] .... 3082.063 2217 bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write
2392 bash-1994 [002] .... 3082.063 2218 bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock
2393 bash-1994 [002] .... 3082.063 2219 bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify
2394 bash-1994 [002] .... 3082.063 2220 bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify
2395 bash-1994 [002] .... 3082.063 2221 bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify
2396 bash-1994 [002] .... 3082.063 2222 bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock
2397 bash-1994 [002] ...1 3082.063 2223 bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock
2398 bash-1994 [002] .... 3082.063 2224 bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify
2399 [...] 2225 [...]
2400 2226
2401 2227
2402 Note: function tracer uses ring buffers to st 2228 Note: function tracer uses ring buffers to store the above
2403 entries. The newest data may overwrite the ol 2229 entries. The newest data may overwrite the oldest data.
2404 Sometimes using echo to stop the trace is not 2230 Sometimes using echo to stop the trace is not sufficient because
2405 the tracing could have overwritten the data t 2231 the tracing could have overwritten the data that you wanted to
2406 record. For this reason, it is sometimes bett 2232 record. For this reason, it is sometimes better to disable
2407 tracing directly from a program. This allows 2233 tracing directly from a program. This allows you to stop the
2408 tracing at the point that you hit the part th 2234 tracing at the point that you hit the part that you are
2409 interested in. To disable the tracing directl 2235 interested in. To disable the tracing directly from a C program,
2410 something like following code snippet can be 2236 something like following code snippet can be used::
2411 2237
2412 int trace_fd; 2238 int trace_fd;
2413 [...] 2239 [...]
2414 int main(int argc, char *argv[]) { 2240 int main(int argc, char *argv[]) {
2415 [...] 2241 [...]
2416 trace_fd = open(tracing_file( 2242 trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
2417 [...] 2243 [...]
2418 if (condition_hit()) { 2244 if (condition_hit()) {
2419 write(trace_fd, "0", 2245 write(trace_fd, "0", 1);
2420 } 2246 }
2421 [...] 2247 [...]
2422 } 2248 }
2423 2249
2424 2250
2425 Single thread tracing 2251 Single thread tracing
2426 --------------------- 2252 ---------------------
2427 2253
2428 By writing into set_ftrace_pid you can trace 2254 By writing into set_ftrace_pid you can trace a
2429 single thread. For example:: 2255 single thread. For example::
2430 2256
2431 # cat set_ftrace_pid 2257 # cat set_ftrace_pid
2432 no pid 2258 no pid
2433 # echo 3111 > set_ftrace_pid 2259 # echo 3111 > set_ftrace_pid
2434 # cat set_ftrace_pid 2260 # cat set_ftrace_pid
2435 3111 2261 3111
2436 # echo function > current_tracer 2262 # echo function > current_tracer
2437 # cat trace | head 2263 # cat trace | head
2438 # tracer: function 2264 # tracer: function
2439 # 2265 #
2440 # TASK-PID CPU# TIMESTAMP 2266 # TASK-PID CPU# TIMESTAMP FUNCTION
2441 # | | | | 2267 # | | | | |
2442 yum-updatesd-3111 [003] 1637.254676: 2268 yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
2443 yum-updatesd-3111 [003] 1637.254681: 2269 yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
2444 yum-updatesd-3111 [003] 1637.254682: 2270 yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
2445 yum-updatesd-3111 [003] 1637.254683: 2271 yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
2446 yum-updatesd-3111 [003] 1637.254685: 2272 yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
2447 yum-updatesd-3111 [003] 1637.254686: 2273 yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
2448 # echo > set_ftrace_pid 2274 # echo > set_ftrace_pid
2449 # cat trace |head 2275 # cat trace |head
2450 # tracer: function 2276 # tracer: function
2451 # 2277 #
2452 # TASK-PID CPU# TIMESTAMP 2278 # TASK-PID CPU# TIMESTAMP FUNCTION
2453 # | | | | 2279 # | | | | |
2454 ##### CPU 3 buffer started #### 2280 ##### CPU 3 buffer started ####
2455 yum-updatesd-3111 [003] 1701.957688: 2281 yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
2456 yum-updatesd-3111 [003] 1701.957689: 2282 yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
2457 yum-updatesd-3111 [003] 1701.957691: 2283 yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
2458 yum-updatesd-3111 [003] 1701.957692: 2284 yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
2459 yum-updatesd-3111 [003] 1701.957693: 2285 yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
2460 2286
2461 If you want to trace a function when executin 2287 If you want to trace a function when executing, you could use
2462 something like this simple program. 2288 something like this simple program.
2463 :: 2289 ::
2464 2290
2465 #include <stdio.h> 2291 #include <stdio.h>
2466 #include <stdlib.h> 2292 #include <stdlib.h>
2467 #include <sys/types.h> 2293 #include <sys/types.h>
2468 #include <sys/stat.h> 2294 #include <sys/stat.h>
2469 #include <fcntl.h> 2295 #include <fcntl.h>
2470 #include <unistd.h> 2296 #include <unistd.h>
2471 #include <string.h> 2297 #include <string.h>
2472 2298
2473 #define _STR(x) #x 2299 #define _STR(x) #x
2474 #define STR(x) _STR(x) 2300 #define STR(x) _STR(x)
2475 #define MAX_PATH 256 2301 #define MAX_PATH 256
2476 2302
2477 const char *find_tracefs(void) 2303 const char *find_tracefs(void)
2478 { 2304 {
2479 static char tracefs[MAX_PATH+1 2305 static char tracefs[MAX_PATH+1];
2480 static int tracefs_found; 2306 static int tracefs_found;
2481 char type[100]; 2307 char type[100];
2482 FILE *fp; 2308 FILE *fp;
2483 2309
2484 if (tracefs_found) 2310 if (tracefs_found)
2485 return tracefs; 2311 return tracefs;
2486 2312
2487 if ((fp = fopen("/proc/mounts" 2313 if ((fp = fopen("/proc/mounts","r")) == NULL) {
2488 perror("/proc/mounts") 2314 perror("/proc/mounts");
2489 return NULL; 2315 return NULL;
2490 } 2316 }
2491 2317
2492 while (fscanf(fp, "%*s %" 2318 while (fscanf(fp, "%*s %"
2493 STR(MAX_PATH) 2319 STR(MAX_PATH)
2494 "s %99s %*s %*d 2320 "s %99s %*s %*d %*d\n",
2495 tracefs, type) = 2321 tracefs, type) == 2) {
2496 if (strcmp(type, "trac 2322 if (strcmp(type, "tracefs") == 0)
2497 break; 2323 break;
2498 } 2324 }
2499 fclose(fp); 2325 fclose(fp);
2500 2326
2501 if (strcmp(type, "tracefs") != 2327 if (strcmp(type, "tracefs") != 0) {
2502 fprintf(stderr, "trace 2328 fprintf(stderr, "tracefs not mounted");
2503 return NULL; 2329 return NULL;
2504 } 2330 }
2505 2331
2506 strcat(tracefs, "/tracing/"); 2332 strcat(tracefs, "/tracing/");
2507 tracefs_found = 1; 2333 tracefs_found = 1;
2508 2334
2509 return tracefs; 2335 return tracefs;
2510 } 2336 }
2511 2337
2512 const char *tracing_file(const char * 2338 const char *tracing_file(const char *file_name)
2513 { 2339 {
2514 static char trace_file[MAX_PAT 2340 static char trace_file[MAX_PATH+1];
2515 snprintf(trace_file, MAX_PATH, 2341 snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name);
2516 return trace_file; 2342 return trace_file;
2517 } 2343 }
2518 2344
2519 int main (int argc, char **argv) 2345 int main (int argc, char **argv)
2520 { 2346 {
2521 if (argc < 1) 2347 if (argc < 1)
2522 exit(-1); 2348 exit(-1);
2523 2349
2524 if (fork() > 0) { 2350 if (fork() > 0) {
2525 int fd, ffd; 2351 int fd, ffd;
2526 char line[64]; 2352 char line[64];
2527 int s; 2353 int s;
2528 2354
2529 ffd = open(tracing_fi 2355 ffd = open(tracing_file("current_tracer"), O_WRONLY);
2530 if (ffd < 0) 2356 if (ffd < 0)
2531 exit(-1); 2357 exit(-1);
2532 write(ffd, "nop", 3); 2358 write(ffd, "nop", 3);
2533 2359
2534 fd = open(tracing_fil 2360 fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
2535 s = sprintf(line, "%d 2361 s = sprintf(line, "%d\n", getpid());
2536 write(fd, line, s); 2362 write(fd, line, s);
2537 2363
2538 write(ffd, "function" 2364 write(ffd, "function", 8);
2539 2365
2540 close(fd); 2366 close(fd);
2541 close(ffd); 2367 close(ffd);
2542 2368
2543 execvp(argv[1], argv+ 2369 execvp(argv[1], argv+1);
2544 } 2370 }
2545 2371
2546 return 0; 2372 return 0;
2547 } 2373 }
2548 2374
2549 Or this simple script! 2375 Or this simple script!
2550 :: 2376 ::
2551 2377
2552 #!/bin/bash 2378 #!/bin/bash
2553 2379
2554 tracefs=`sed -ne 's/^tracefs \(.*\) tracefs 2380 tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts`
2555 echo 0 > $tracefs/tracing_on !! 2381 echo nop > $tracefs/tracing/current_tracer
2556 echo $$ > $tracefs/set_ftrace_pid !! 2382 echo 0 > $tracefs/tracing/tracing_on
2557 echo function > $tracefs/current_tracer !! 2383 echo $$ > $tracefs/tracing/set_ftrace_pid
2558 echo 1 > $tracefs/tracing_on !! 2384 echo function > $tracefs/tracing/current_tracer
>> 2385 echo 1 > $tracefs/tracing/tracing_on
2559 exec "$@" 2386 exec "$@"
2560 2387
2561 2388
2562 function graph tracer 2389 function graph tracer
2563 --------------------------- 2390 ---------------------------
2564 2391
2565 This tracer is similar to the function tracer 2392 This tracer is similar to the function tracer except that it
2566 probes a function on its entry and its exit. 2393 probes a function on its entry and its exit. This is done by
2567 using a dynamically allocated stack of return 2394 using a dynamically allocated stack of return addresses in each
2568 task_struct. On function entry the tracer ove 2395 task_struct. On function entry the tracer overwrites the return
2569 address of each function traced to set a cust 2396 address of each function traced to set a custom probe. Thus the
2570 original return address is stored on the stac 2397 original return address is stored on the stack of return address
2571 in the task_struct. 2398 in the task_struct.
2572 2399
2573 Probing on both ends of a function leads to s 2400 Probing on both ends of a function leads to special features
2574 such as: 2401 such as:
2575 2402
2576 - measure of a function's time execution 2403 - measure of a function's time execution
2577 - having a reliable call stack to draw functi 2404 - having a reliable call stack to draw function calls graph
2578 2405
2579 This tracer is useful in several situations: 2406 This tracer is useful in several situations:
2580 2407
2581 - you want to find the reason of a strange ke 2408 - you want to find the reason of a strange kernel behavior and
2582 need to see what happens in detail on any a 2409 need to see what happens in detail on any areas (or specific
2583 ones). 2410 ones).
2584 2411
2585 - you are experiencing weird latencies but it 2412 - you are experiencing weird latencies but it's difficult to
2586 find its origin. 2413 find its origin.
2587 2414
2588 - you want to find quickly which path is take 2415 - you want to find quickly which path is taken by a specific
2589 function 2416 function
2590 2417
2591 - you just want to peek inside a working kern 2418 - you just want to peek inside a working kernel and want to see
2592 what happens there. 2419 what happens there.
2593 2420
2594 :: 2421 ::
2595 2422
2596 # tracer: function_graph 2423 # tracer: function_graph
2597 # 2424 #
2598 # CPU DURATION FUNCTION C 2425 # CPU DURATION FUNCTION CALLS
2599 # | | | | | | 2426 # | | | | | | |
2600 2427
2601 0) | sys_open() { 2428 0) | sys_open() {
2602 0) | do_sys_open() { 2429 0) | do_sys_open() {
2603 0) | getname() { 2430 0) | getname() {
2604 0) | kmem_cache_alloc 2431 0) | kmem_cache_alloc() {
2605 0) 1.382 us | __might_sleep( 2432 0) 1.382 us | __might_sleep();
2606 0) 2.478 us | } 2433 0) 2.478 us | }
2607 0) | strncpy_from_use 2434 0) | strncpy_from_user() {
2608 0) | might_fault() 2435 0) | might_fault() {
2609 0) 1.389 us | __might_slee 2436 0) 1.389 us | __might_sleep();
2610 0) 2.553 us | } 2437 0) 2.553 us | }
2611 0) 3.807 us | } 2438 0) 3.807 us | }
2612 0) 7.876 us | } 2439 0) 7.876 us | }
2613 0) | alloc_fd() { 2440 0) | alloc_fd() {
2614 0) 0.668 us | _spin_lock(); 2441 0) 0.668 us | _spin_lock();
2615 0) 0.570 us | expand_files(); 2442 0) 0.570 us | expand_files();
2616 0) 0.586 us | _spin_unlock(); 2443 0) 0.586 us | _spin_unlock();
2617 2444
2618 2445
2619 There are several columns that can be dynamic 2446 There are several columns that can be dynamically
2620 enabled/disabled. You can use every combinati 2447 enabled/disabled. You can use every combination of options you
2621 want, depending on your needs. 2448 want, depending on your needs.
2622 2449
2623 - The cpu number on which the function execut 2450 - The cpu number on which the function executed is default
2624 enabled. It is sometimes better to only tr 2451 enabled. It is sometimes better to only trace one cpu (see
2625 tracing_cpumask file) or you might sometime !! 2452 tracing_cpu_mask file) or you might sometimes see unordered
2626 function calls while cpu tracing switch. 2453 function calls while cpu tracing switch.
2627 2454
2628 - hide: echo nofuncgraph-cpu > trace_ 2455 - hide: echo nofuncgraph-cpu > trace_options
2629 - show: echo funcgraph-cpu > trace_op 2456 - show: echo funcgraph-cpu > trace_options
2630 2457
2631 - The duration (function's time of execution) 2458 - The duration (function's time of execution) is displayed on
2632 the closing bracket line of a function or o 2459 the closing bracket line of a function or on the same line
2633 than the current function in case of a leaf 2460 than the current function in case of a leaf one. It is default
2634 enabled. 2461 enabled.
2635 2462
2636 - hide: echo nofuncgraph-duration > t 2463 - hide: echo nofuncgraph-duration > trace_options
2637 - show: echo funcgraph-duration > tra 2464 - show: echo funcgraph-duration > trace_options
2638 2465
2639 - The overhead field precedes the duration fi 2466 - The overhead field precedes the duration field in case of
2640 reached duration thresholds. 2467 reached duration thresholds.
2641 2468
2642 - hide: echo nofuncgraph-overhead > t 2469 - hide: echo nofuncgraph-overhead > trace_options
2643 - show: echo funcgraph-overhead > tra 2470 - show: echo funcgraph-overhead > trace_options
2644 - depends on: funcgraph-duration 2471 - depends on: funcgraph-duration
2645 2472
2646 ie:: 2473 ie::
2647 2474
2648 3) # 1837.709 us | } /* __switch 2475 3) # 1837.709 us | } /* __switch_to */
2649 3) | finish_task_s 2476 3) | finish_task_switch() {
2650 3) 0.313 us | _raw_spin_u 2477 3) 0.313 us | _raw_spin_unlock_irq();
2651 3) 3.177 us | } 2478 3) 3.177 us | }
2652 3) # 1889.063 us | } /* __schedule 2479 3) # 1889.063 us | } /* __schedule */
2653 3) ! 140.417 us | } /* __schedule * 2480 3) ! 140.417 us | } /* __schedule */
2654 3) # 2034.948 us | } /* schedule */ 2481 3) # 2034.948 us | } /* schedule */
2655 3) * 33998.59 us | } /* schedule_preempt 2482 3) * 33998.59 us | } /* schedule_preempt_disabled */
2656 2483
2657 [...] 2484 [...]
2658 2485
2659 1) 0.260 us | msecs_to_ 2486 1) 0.260 us | msecs_to_jiffies();
2660 1) 0.313 us | __rcu_rea 2487 1) 0.313 us | __rcu_read_unlock();
2661 1) + 61.770 us | } 2488 1) + 61.770 us | }
2662 1) + 64.479 us | } 2489 1) + 64.479 us | }
2663 1) 0.313 us | rcu_bh_qs(); 2490 1) 0.313 us | rcu_bh_qs();
2664 1) 0.313 us | __local_bh_en 2491 1) 0.313 us | __local_bh_enable();
2665 1) ! 217.240 us | } 2492 1) ! 217.240 us | }
2666 1) 0.365 us | idle_cpu(); 2493 1) 0.365 us | idle_cpu();
2667 1) | rcu_irq_exit() 2494 1) | rcu_irq_exit() {
2668 1) 0.417 us | rcu_eqs_enter 2495 1) 0.417 us | rcu_eqs_enter_common.isra.47();
2669 1) 3.125 us | } 2496 1) 3.125 us | }
2670 1) ! 227.812 us | } 2497 1) ! 227.812 us | }
2671 1) ! 457.395 us | } 2498 1) ! 457.395 us | }
2672 1) @ 119760.2 us | } 2499 1) @ 119760.2 us | }
2673 2500
2674 [...] 2501 [...]
2675 2502
2676 2) | handle_IPI() { 2503 2) | handle_IPI() {
2677 1) 6.979 us | } 2504 1) 6.979 us | }
2678 2) 0.417 us | scheduler_ipi(); 2505 2) 0.417 us | scheduler_ipi();
2679 1) 9.791 us | } 2506 1) 9.791 us | }
2680 1) + 12.917 us | } 2507 1) + 12.917 us | }
2681 2) 3.490 us | } 2508 2) 3.490 us | }
2682 1) + 15.729 us | } 2509 1) + 15.729 us | }
2683 1) + 18.542 us | } 2510 1) + 18.542 us | }
2684 2) $ 3594274 us | } 2511 2) $ 3594274 us | }
2685 2512
2686 Flags:: 2513 Flags::
2687 2514
2688 + means that the function exceeded 10 usecs 2515 + means that the function exceeded 10 usecs.
2689 ! means that the function exceeded 100 usec 2516 ! means that the function exceeded 100 usecs.
2690 # means that the function exceeded 1000 use 2517 # means that the function exceeded 1000 usecs.
2691 * means that the function exceeded 10 msecs 2518 * means that the function exceeded 10 msecs.
2692 @ means that the function exceeded 100 msec 2519 @ means that the function exceeded 100 msecs.
2693 $ means that the function exceeded 1 sec. 2520 $ means that the function exceeded 1 sec.
2694 2521
2695 2522
2696 - The task/pid field displays the thread cmdl 2523 - The task/pid field displays the thread cmdline and pid which
2697 executed the function. It is default disabl 2524 executed the function. It is default disabled.
2698 2525
2699 - hide: echo nofuncgraph-proc > trace 2526 - hide: echo nofuncgraph-proc > trace_options
2700 - show: echo funcgraph-proc > trace_o 2527 - show: echo funcgraph-proc > trace_options
2701 2528
2702 ie:: 2529 ie::
2703 2530
2704 # tracer: function_graph 2531 # tracer: function_graph
2705 # 2532 #
2706 # CPU TASK/PID DURATION 2533 # CPU TASK/PID DURATION FUNCTION CALLS
2707 # | | | | | 2534 # | | | | | | | | |
2708 0) sh-4802 | | 2535 0) sh-4802 | | d_free() {
2709 0) sh-4802 | | 2536 0) sh-4802 | | call_rcu() {
2710 0) sh-4802 | | 2537 0) sh-4802 | | __call_rcu() {
2711 0) sh-4802 | 0.616 us | 2538 0) sh-4802 | 0.616 us | rcu_process_gp_end();
2712 0) sh-4802 | 0.586 us | 2539 0) sh-4802 | 0.586 us | check_for_new_grace_period();
2713 0) sh-4802 | 2.899 us | 2540 0) sh-4802 | 2.899 us | }
2714 0) sh-4802 | 4.040 us | 2541 0) sh-4802 | 4.040 us | }
2715 0) sh-4802 | 5.151 us | 2542 0) sh-4802 | 5.151 us | }
2716 0) sh-4802 | + 49.370 us | 2543 0) sh-4802 | + 49.370 us | }
2717 2544
2718 2545
2719 - The absolute time field is an absolute time 2546 - The absolute time field is an absolute timestamp given by the
2720 system clock since it started. A snapshot o 2547 system clock since it started. A snapshot of this time is
2721 given on each entry/exit of functions 2548 given on each entry/exit of functions
2722 2549
2723 - hide: echo nofuncgraph-abstime > tr 2550 - hide: echo nofuncgraph-abstime > trace_options
2724 - show: echo funcgraph-abstime > trac 2551 - show: echo funcgraph-abstime > trace_options
2725 2552
2726 ie:: 2553 ie::
2727 2554
2728 # 2555 #
2729 # TIME CPU DURATION 2556 # TIME CPU DURATION FUNCTION CALLS
2730 # | | | | 2557 # | | | | | | | |
2731 360.774522 | 1) 0.541 us | 2558 360.774522 | 1) 0.541 us | }
2732 360.774522 | 1) 4.663 us | 2559 360.774522 | 1) 4.663 us | }
2733 360.774523 | 1) 0.541 us | 2560 360.774523 | 1) 0.541 us | __wake_up_bit();
2734 360.774524 | 1) 6.796 us | 2561 360.774524 | 1) 6.796 us | }
2735 360.774524 | 1) 7.952 us | 2562 360.774524 | 1) 7.952 us | }
2736 360.774525 | 1) 9.063 us | 2563 360.774525 | 1) 9.063 us | }
2737 360.774525 | 1) 0.615 us | 2564 360.774525 | 1) 0.615 us | journal_mark_dirty();
2738 360.774527 | 1) 0.578 us | 2565 360.774527 | 1) 0.578 us | __brelse();
2739 360.774528 | 1) | 2566 360.774528 | 1) | reiserfs_prepare_for_journal() {
2740 360.774528 | 1) | 2567 360.774528 | 1) | unlock_buffer() {
2741 360.774529 | 1) | 2568 360.774529 | 1) | wake_up_bit() {
2742 360.774529 | 1) | 2569 360.774529 | 1) | bit_waitqueue() {
2743 360.774530 | 1) 0.594 us | 2570 360.774530 | 1) 0.594 us | __phys_addr();
2744 2571
2745 2572
2746 The function name is always displayed after t 2573 The function name is always displayed after the closing bracket
2747 for a function if the start of that function 2574 for a function if the start of that function is not in the
2748 trace buffer. 2575 trace buffer.
2749 2576
2750 Display of the function name after the closin 2577 Display of the function name after the closing bracket may be
2751 enabled for functions whose start is in the t 2578 enabled for functions whose start is in the trace buffer,
2752 allowing easier searching with grep for funct 2579 allowing easier searching with grep for function durations.
2753 It is default disabled. 2580 It is default disabled.
2754 2581
2755 - hide: echo nofuncgraph-tail > trace 2582 - hide: echo nofuncgraph-tail > trace_options
2756 - show: echo funcgraph-tail > trace_o 2583 - show: echo funcgraph-tail > trace_options
2757 2584
2758 Example with nofuncgraph-tail (default):: 2585 Example with nofuncgraph-tail (default)::
2759 2586
2760 0) | putname() { 2587 0) | putname() {
2761 0) | kmem_cache_free 2588 0) | kmem_cache_free() {
2762 0) 0.518 us | __phys_addr() 2589 0) 0.518 us | __phys_addr();
2763 0) 1.757 us | } 2590 0) 1.757 us | }
2764 0) 2.861 us | } 2591 0) 2.861 us | }
2765 2592
2766 Example with funcgraph-tail:: 2593 Example with funcgraph-tail::
2767 2594
2768 0) | putname() { 2595 0) | putname() {
2769 0) | kmem_cache_free 2596 0) | kmem_cache_free() {
2770 0) 0.518 us | __phys_addr() 2597 0) 0.518 us | __phys_addr();
2771 0) 1.757 us | } /* kmem_cache 2598 0) 1.757 us | } /* kmem_cache_free() */
2772 0) 2.861 us | } /* putname() */ 2599 0) 2.861 us | } /* putname() */
2773 2600
2774 The return value of each traced function can <<
2775 an equal sign "=". When encountering system c <<
2776 can be very helpful to quickly locate the fun <<
2777 returns an error code. <<
2778 <<
2779 - hide: echo nofuncgraph-retval > tra <<
2780 - show: echo funcgraph-retval > trace <<
2781 <<
2782 Example with funcgraph-retval:: <<
2783 <<
2784 1) | cgroup_migrate() { <<
2785 1) 0.651 us | cgroup_migrate_ad <<
2786 1) | cgroup_migrate_ex <<
2787 1) | cpu_cgroup_can_ <<
2788 1) | cgroup_taskse <<
2789 1) 0.732 us | cgroup_task <<
2790 1) 1.232 us | } /* cgroup_t <<
2791 1) 0.380 us | sched_rt_can_ <<
2792 1) 2.335 us | } /* cpu_cgroup <<
2793 1) 4.369 us | } /* cgroup_migra <<
2794 1) 7.143 us | } /* cgroup_migrate <<
2795 <<
2796 The above example shows that the function cpu <<
2797 returned the error code -22 firstly, then we <<
2798 of this function to get the root cause. <<
2799 <<
2800 When the option funcgraph-retval-hex is not s <<
2801 be displayed in a smart way. Specifically, if <<
2802 it will be printed in signed decimal format, <<
2803 printed in hexadecimal format. <<
2804 <<
2805 - smart: echo nofuncgraph-retval-hex <<
2806 - hexadecimal: echo funcgraph-retval- <<
2807 <<
2808 Example with funcgraph-retval-hex:: <<
2809 <<
2810 1) | cgroup_migrate() <<
2811 1) 0.651 us | cgroup_migrate_ <<
2812 1) | cgroup_migrate_ <<
2813 1) | cpu_cgroup_ca <<
2814 1) | cgroup_task <<
2815 1) 0.732 us | cgroup_ta <<
2816 1) 1.232 us | } /* cgroup <<
2817 1) 0.380 us | sched_rt_ca <<
2818 1) 2.335 us | } /* cpu_cgro <<
2819 1) 4.369 us | } /* cgroup_mig <<
2820 1) 7.143 us | } /* cgroup_migra <<
2821 <<
2822 At present, there are some limitations when u <<
2823 option, and these limitations will be elimina <<
2824 <<
2825 - Even if the function return type is void, a <<
2826 be printed, and you can just ignore it. <<
2827 <<
2828 - Even if return values are stored in multipl <<
2829 value contained in the first register will <<
2830 To illustrate, in the x86 architecture, eax <<
2831 a 64-bit return value, with the lower 32 bi <<
2832 upper 32 bits saved in edx. However, only t <<
2833 will be recorded and printed. <<
2834 <<
2835 - In certain procedure call standards, such a <<
2836 type is smaller than a GPR, it is the respo <<
2837 to perform the narrowing, and the upper bit <<
2838 Therefore, it is advisable to check the cod <<
2839 when using a u8 in a 64-bit GPR, bits [63:8 <<
2840 especially when larger types are truncated, <<
2841 Here are some specific cases to illustrate <<
2842 <<
2843 **Case One**: <<
2844 <<
2845 The function narrow_to_u8 is defined as fol <<
2846 <<
2847 u8 narrow_to_u8(u64 val) <<
2848 { <<
2849 // implicitly truncated <<
2850 return val; <<
2851 } <<
2852 <<
2853 It may be compiled to:: <<
2854 <<
2855 narrow_to_u8: <<
2856 < ... ftrace instrumentation <<
2857 RET <<
2858 <<
2859 If you pass 0x123456789abcdef to this funct <<
2860 it may be recorded as 0x123456789abcdef ins <<
2861 <<
2862 **Case Two**: <<
2863 <<
2864 The function error_if_not_4g_aligned is def <<
2865 <<
2866 int error_if_not_4g_aligned(u64 val) <<
2867 { <<
2868 if (val & GENMASK(31, 0)) <<
2869 return -EINVAL; <<
2870 <<
2871 return 0; <<
2872 } <<
2873 <<
2874 It could be compiled to:: <<
2875 <<
2876 error_if_not_4g_aligned: <<
2877 CBNZ w0, .Lnot_aligned <<
2878 RET // bi <<
2879 // [6 <<
2880 .Lnot_aligned: <<
2881 MOV x0, #-EINVAL <<
2882 RET <<
2883 <<
2884 When passing 0x2_0000_0000 to it, the retur <<
2885 0x2_0000_0000 instead of 0. <<
2886 <<
2887 You can put some comments on specific functio 2601 You can put some comments on specific functions by using
2888 trace_printk() For example, if you want to pu 2602 trace_printk() For example, if you want to put a comment inside
2889 the __might_sleep() function, you just have t 2603 the __might_sleep() function, you just have to include
2890 <linux/ftrace.h> and call trace_printk() insi 2604 <linux/ftrace.h> and call trace_printk() inside __might_sleep()::
2891 2605
2892 trace_printk("I'm a comment!\n") 2606 trace_printk("I'm a comment!\n")
2893 2607
2894 will produce:: 2608 will produce::
2895 2609
2896 1) | __might_sle 2610 1) | __might_sleep() {
2897 1) | /* I'm a 2611 1) | /* I'm a comment! */
2898 1) 1.449 us | } 2612 1) 1.449 us | }
2899 2613
2900 2614
2901 You might find other useful features for this 2615 You might find other useful features for this tracer in the
2902 following "dynamic ftrace" section such as tr 2616 following "dynamic ftrace" section such as tracing only specific
2903 functions or tasks. 2617 functions or tasks.
2904 2618
2905 dynamic ftrace 2619 dynamic ftrace
2906 -------------- 2620 --------------
2907 2621
2908 If CONFIG_DYNAMIC_FTRACE is set, the system w 2622 If CONFIG_DYNAMIC_FTRACE is set, the system will run with
2909 virtually no overhead when function tracing i 2623 virtually no overhead when function tracing is disabled. The way
2910 this works is the mcount function call (place 2624 this works is the mcount function call (placed at the start of
2911 every kernel function, produced by the -pg sw 2625 every kernel function, produced by the -pg switch in gcc),
2912 starts of pointing to a simple return. (Enabl 2626 starts of pointing to a simple return. (Enabling FTRACE will
2913 include the -pg switch in the compiling of th 2627 include the -pg switch in the compiling of the kernel.)
2914 2628
2915 At compile time every C file object is run th 2629 At compile time every C file object is run through the
2916 recordmcount program (located in the scripts 2630 recordmcount program (located in the scripts directory). This
2917 program will parse the ELF headers in the C o 2631 program will parse the ELF headers in the C object to find all
2918 the locations in the .text section that call 2632 the locations in the .text section that call mcount. Starting
2919 with gcc version 4.6, the -mfentry has been a 2633 with gcc version 4.6, the -mfentry has been added for x86, which
2920 calls "__fentry__" instead of "mcount". Which 2634 calls "__fentry__" instead of "mcount". Which is called before
2921 the creation of the stack frame. 2635 the creation of the stack frame.
2922 2636
2923 Note, not all sections are traced. They may b 2637 Note, not all sections are traced. They may be prevented by either
2924 a notrace, or blocked another way and all inl 2638 a notrace, or blocked another way and all inline functions are not
2925 traced. Check the "available_filter_functions 2639 traced. Check the "available_filter_functions" file to see what functions
2926 can be traced. 2640 can be traced.
2927 2641
2928 A section called "__mcount_loc" is created th 2642 A section called "__mcount_loc" is created that holds
2929 references to all the mcount/fentry call site 2643 references to all the mcount/fentry call sites in the .text section.
2930 The recordmcount program re-links this sectio 2644 The recordmcount program re-links this section back into the
2931 original object. The final linking stage of t 2645 original object. The final linking stage of the kernel will add all these
2932 references into a single table. 2646 references into a single table.
2933 2647
2934 On boot up, before SMP is initialized, the dy 2648 On boot up, before SMP is initialized, the dynamic ftrace code
2935 scans this table and updates all the location 2649 scans this table and updates all the locations into nops. It
2936 also records the locations, which are added t 2650 also records the locations, which are added to the
2937 available_filter_functions list. Modules are 2651 available_filter_functions list. Modules are processed as they
2938 are loaded and before they are executed. Whe 2652 are loaded and before they are executed. When a module is
2939 unloaded, it also removes its functions from 2653 unloaded, it also removes its functions from the ftrace function
2940 list. This is automatic in the module unload 2654 list. This is automatic in the module unload code, and the
2941 module author does not need to worry about it 2655 module author does not need to worry about it.
2942 2656
2943 When tracing is enabled, the process of modif 2657 When tracing is enabled, the process of modifying the function
2944 tracepoints is dependent on architecture. The 2658 tracepoints is dependent on architecture. The old method is to use
2945 kstop_machine to prevent races with the CPUs 2659 kstop_machine to prevent races with the CPUs executing code being
2946 modified (which can cause the CPU to do undes 2660 modified (which can cause the CPU to do undesirable things, especially
2947 if the modified code crosses cache (or page) 2661 if the modified code crosses cache (or page) boundaries), and the nops are
2948 patched back to calls. But this time, they do 2662 patched back to calls. But this time, they do not call mcount
2949 (which is just a function stub). They now cal 2663 (which is just a function stub). They now call into the ftrace
2950 infrastructure. 2664 infrastructure.
2951 2665
2952 The new method of modifying the function trac 2666 The new method of modifying the function tracepoints is to place
2953 a breakpoint at the location to be modified, 2667 a breakpoint at the location to be modified, sync all CPUs, modify
2954 the rest of the instruction not covered by th 2668 the rest of the instruction not covered by the breakpoint. Sync
2955 all CPUs again, and then remove the breakpoin 2669 all CPUs again, and then remove the breakpoint with the finished
2956 version to the ftrace call site. 2670 version to the ftrace call site.
2957 2671
2958 Some archs do not even need to monkey around 2672 Some archs do not even need to monkey around with the synchronization,
2959 and can just slap the new code on top of the 2673 and can just slap the new code on top of the old without any
2960 problems with other CPUs executing it at the 2674 problems with other CPUs executing it at the same time.
2961 2675
2962 One special side-effect to the recording of t 2676 One special side-effect to the recording of the functions being
2963 traced is that we can now selectively choose 2677 traced is that we can now selectively choose which functions we
2964 wish to trace and which ones we want the mcou 2678 wish to trace and which ones we want the mcount calls to remain
2965 as nops. 2679 as nops.
2966 2680
2967 Two files are used, one for enabling and one 2681 Two files are used, one for enabling and one for disabling the
2968 tracing of specified functions. They are: 2682 tracing of specified functions. They are:
2969 2683
2970 set_ftrace_filter 2684 set_ftrace_filter
2971 2685
2972 and 2686 and
2973 2687
2974 set_ftrace_notrace 2688 set_ftrace_notrace
2975 2689
2976 A list of available functions that you can ad 2690 A list of available functions that you can add to these files is
2977 listed in: 2691 listed in:
2978 2692
2979 available_filter_functions 2693 available_filter_functions
2980 2694
2981 :: 2695 ::
2982 2696
2983 # cat available_filter_functions 2697 # cat available_filter_functions
2984 put_prev_task_idle 2698 put_prev_task_idle
2985 kmem_cache_create 2699 kmem_cache_create
2986 pick_next_task_rt 2700 pick_next_task_rt
2987 cpus_read_lock !! 2701 get_online_cpus
2988 pick_next_task_fair 2702 pick_next_task_fair
2989 mutex_lock 2703 mutex_lock
2990 [...] 2704 [...]
2991 2705
2992 If I am only interested in sys_nanosleep and 2706 If I am only interested in sys_nanosleep and hrtimer_interrupt::
2993 2707
2994 # echo sys_nanosleep hrtimer_interrupt > se 2708 # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
2995 # echo function > current_tracer 2709 # echo function > current_tracer
2996 # echo 1 > tracing_on 2710 # echo 1 > tracing_on
2997 # usleep 1 2711 # usleep 1
2998 # echo 0 > tracing_on 2712 # echo 0 > tracing_on
2999 # cat trace 2713 # cat trace
3000 # tracer: function 2714 # tracer: function
3001 # 2715 #
3002 # entries-in-buffer/entries-written: 5/5 2716 # entries-in-buffer/entries-written: 5/5 #P:4
3003 # 2717 #
3004 # _-----=> irq 2718 # _-----=> irqs-off
3005 # / _----=> nee 2719 # / _----=> need-resched
3006 # | / _---=> har 2720 # | / _---=> hardirq/softirq
3007 # || / _--=> pre 2721 # || / _--=> preempt-depth
3008 # ||| / dela 2722 # ||| / delay
3009 # TASK-PID CPU# |||| TIMEST 2723 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3010 # | | | |||| | 2724 # | | | |||| | |
3011 usleep-2665 [001] .... 4186.475 2725 usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath
3012 <idle>-0 [001] d.h1 4186.475 2726 <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
3013 usleep-2665 [001] d.h1 4186.475 2727 usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
3014 <idle>-0 [003] d.h1 4186.475 2728 <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
3015 <idle>-0 [002] d.h1 4186.475 2729 <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
3016 2730
3017 To see which functions are being traced, you 2731 To see which functions are being traced, you can cat the file:
3018 :: 2732 ::
3019 2733
3020 # cat set_ftrace_filter 2734 # cat set_ftrace_filter
3021 hrtimer_interrupt 2735 hrtimer_interrupt
3022 sys_nanosleep 2736 sys_nanosleep
3023 2737
3024 2738
3025 Perhaps this is not enough. The filters also 2739 Perhaps this is not enough. The filters also allow glob(7) matching.
3026 2740
3027 ``<match>*`` 2741 ``<match>*``
3028 will match functions that begin with 2742 will match functions that begin with <match>
3029 ``*<match>`` 2743 ``*<match>``
3030 will match functions that end with <m 2744 will match functions that end with <match>
3031 ``*<match>*`` 2745 ``*<match>*``
3032 will match functions that have <match 2746 will match functions that have <match> in it
3033 ``<match1>*<match2>`` 2747 ``<match1>*<match2>``
3034 will match functions that begin with 2748 will match functions that begin with <match1> and end with <match2>
3035 2749
3036 .. note:: 2750 .. note::
3037 It is better to use quotes to enclose t 2751 It is better to use quotes to enclose the wild cards,
3038 otherwise the shell may expand the para 2752 otherwise the shell may expand the parameters into names
3039 of files in the local directory. 2753 of files in the local directory.
3040 2754
3041 :: 2755 ::
3042 2756
3043 # echo 'hrtimer_*' > set_ftrace_filter 2757 # echo 'hrtimer_*' > set_ftrace_filter
3044 2758
3045 Produces:: 2759 Produces::
3046 2760
3047 # tracer: function 2761 # tracer: function
3048 # 2762 #
3049 # entries-in-buffer/entries-written: 897/89 2763 # entries-in-buffer/entries-written: 897/897 #P:4
3050 # 2764 #
3051 # _-----=> irq 2765 # _-----=> irqs-off
3052 # / _----=> nee 2766 # / _----=> need-resched
3053 # | / _---=> har 2767 # | / _---=> hardirq/softirq
3054 # || / _--=> pre 2768 # || / _--=> preempt-depth
3055 # ||| / dela 2769 # ||| / delay
3056 # TASK-PID CPU# |||| TIMEST 2770 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3057 # | | | |||| | 2771 # | | | |||| | |
3058 <idle>-0 [003] dN.1 4228.547 2772 <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
3059 <idle>-0 [003] dN.1 4228.547 2773 <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
3060 <idle>-0 [003] dN.2 4228.547 2774 <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
3061 <idle>-0 [003] dN.1 4228.547 2775 <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit
3062 <idle>-0 [003] dN.1 4228.547 2776 <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
3063 <idle>-0 [003] d..1 4228.547 2777 <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
3064 <idle>-0 [003] d..1 4228.547 2778 <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter
3065 <idle>-0 [003] d..2 4228.547 2779 <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem
3066 2780
3067 Notice that we lost the sys_nanosleep. 2781 Notice that we lost the sys_nanosleep.
3068 :: 2782 ::
3069 2783
3070 # cat set_ftrace_filter 2784 # cat set_ftrace_filter
3071 hrtimer_run_queues 2785 hrtimer_run_queues
3072 hrtimer_run_pending 2786 hrtimer_run_pending
3073 hrtimer_init 2787 hrtimer_init
3074 hrtimer_cancel 2788 hrtimer_cancel
3075 hrtimer_try_to_cancel 2789 hrtimer_try_to_cancel
3076 hrtimer_forward 2790 hrtimer_forward
3077 hrtimer_start 2791 hrtimer_start
3078 hrtimer_reprogram 2792 hrtimer_reprogram
3079 hrtimer_force_reprogram 2793 hrtimer_force_reprogram
3080 hrtimer_get_next_event 2794 hrtimer_get_next_event
3081 hrtimer_interrupt 2795 hrtimer_interrupt
3082 hrtimer_nanosleep 2796 hrtimer_nanosleep
3083 hrtimer_wakeup 2797 hrtimer_wakeup
3084 hrtimer_get_remaining 2798 hrtimer_get_remaining
3085 hrtimer_get_res 2799 hrtimer_get_res
3086 hrtimer_init_sleeper 2800 hrtimer_init_sleeper
3087 2801
3088 2802
3089 This is because the '>' and '>>' act just lik 2803 This is because the '>' and '>>' act just like they do in bash.
3090 To rewrite the filters, use '>' 2804 To rewrite the filters, use '>'
3091 To append to the filters, use '>>' 2805 To append to the filters, use '>>'
3092 2806
3093 To clear out a filter so that all functions w 2807 To clear out a filter so that all functions will be recorded
3094 again:: 2808 again::
3095 2809
3096 # echo > set_ftrace_filter 2810 # echo > set_ftrace_filter
3097 # cat set_ftrace_filter 2811 # cat set_ftrace_filter
3098 # 2812 #
3099 2813
3100 Again, now we want to append. 2814 Again, now we want to append.
3101 2815
3102 :: 2816 ::
3103 2817
3104 # echo sys_nanosleep > set_ftrace_filter 2818 # echo sys_nanosleep > set_ftrace_filter
3105 # cat set_ftrace_filter 2819 # cat set_ftrace_filter
3106 sys_nanosleep 2820 sys_nanosleep
3107 # echo 'hrtimer_*' >> set_ftrace_filter 2821 # echo 'hrtimer_*' >> set_ftrace_filter
3108 # cat set_ftrace_filter 2822 # cat set_ftrace_filter
3109 hrtimer_run_queues 2823 hrtimer_run_queues
3110 hrtimer_run_pending 2824 hrtimer_run_pending
3111 hrtimer_init 2825 hrtimer_init
3112 hrtimer_cancel 2826 hrtimer_cancel
3113 hrtimer_try_to_cancel 2827 hrtimer_try_to_cancel
3114 hrtimer_forward 2828 hrtimer_forward
3115 hrtimer_start 2829 hrtimer_start
3116 hrtimer_reprogram 2830 hrtimer_reprogram
3117 hrtimer_force_reprogram 2831 hrtimer_force_reprogram
3118 hrtimer_get_next_event 2832 hrtimer_get_next_event
3119 hrtimer_interrupt 2833 hrtimer_interrupt
3120 sys_nanosleep 2834 sys_nanosleep
3121 hrtimer_nanosleep 2835 hrtimer_nanosleep
3122 hrtimer_wakeup 2836 hrtimer_wakeup
3123 hrtimer_get_remaining 2837 hrtimer_get_remaining
3124 hrtimer_get_res 2838 hrtimer_get_res
3125 hrtimer_init_sleeper 2839 hrtimer_init_sleeper
3126 2840
3127 2841
3128 The set_ftrace_notrace prevents those functio 2842 The set_ftrace_notrace prevents those functions from being
3129 traced. 2843 traced.
3130 :: 2844 ::
3131 2845
3132 # echo '*preempt*' '*lock*' > set_ftrace_no 2846 # echo '*preempt*' '*lock*' > set_ftrace_notrace
3133 2847
3134 Produces:: 2848 Produces::
3135 2849
3136 # tracer: function 2850 # tracer: function
3137 # 2851 #
3138 # entries-in-buffer/entries-written: 39608/ 2852 # entries-in-buffer/entries-written: 39608/39608 #P:4
3139 # 2853 #
3140 # _-----=> irq 2854 # _-----=> irqs-off
3141 # / _----=> nee 2855 # / _----=> need-resched
3142 # | / _---=> har 2856 # | / _---=> hardirq/softirq
3143 # || / _--=> pre 2857 # || / _--=> preempt-depth
3144 # ||| / dela 2858 # ||| / delay
3145 # TASK-PID CPU# |||| TIMEST 2859 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3146 # | | | |||| | 2860 # | | | |||| | |
3147 bash-1994 [000] .... 4342.324 2861 bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open
3148 bash-1994 [000] .... 4342.324 2862 bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last
3149 bash-1994 [000] .... 4342.324 2863 bash-1994 [000] .... 4342.324897: ima_file_check <-do_last
3150 bash-1994 [000] .... 4342.324 2864 bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check
3151 bash-1994 [000] .... 4342.324 2865 bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement
3152 bash-1994 [000] .... 4342.324 2866 bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action
3153 bash-1994 [000] .... 4342.324 2867 bash-1994 [000] .... 4342.324899: do_truncate <-do_last
3154 bash-1994 [000] .... 4342.324 !! 2868 bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate
3155 bash-1994 [000] .... 4342.324 2869 bash-1994 [000] .... 4342.324899: notify_change <-do_truncate
3156 bash-1994 [000] .... 4342.324 2870 bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change
3157 bash-1994 [000] .... 4342.324 2871 bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time
3158 bash-1994 [000] .... 4342.324 2872 bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time
3159 2873
3160 We can see that there's no more lock or preem 2874 We can see that there's no more lock or preempt tracing.
3161 2875
3162 Selecting function filters via index 2876 Selecting function filters via index
3163 ------------------------------------ 2877 ------------------------------------
3164 2878
3165 Because processing of strings is expensive (t 2879 Because processing of strings is expensive (the address of the function
3166 needs to be looked up before comparing to the 2880 needs to be looked up before comparing to the string being passed in),
3167 an index can be used as well to enable functi 2881 an index can be used as well to enable functions. This is useful in the
3168 case of setting thousands of specific functio 2882 case of setting thousands of specific functions at a time. By passing
3169 in a list of numbers, no string processing wi 2883 in a list of numbers, no string processing will occur. Instead, the function
3170 at the specific location in the internal arra 2884 at the specific location in the internal array (which corresponds to the
3171 functions in the "available_filter_functions" 2885 functions in the "available_filter_functions" file), is selected.
3172 2886
3173 :: 2887 ::
3174 2888
3175 # echo 1 > set_ftrace_filter 2889 # echo 1 > set_ftrace_filter
3176 2890
3177 Will select the first function listed in "ava 2891 Will select the first function listed in "available_filter_functions"
3178 2892
3179 :: 2893 ::
3180 2894
3181 # head -1 available_filter_functions 2895 # head -1 available_filter_functions
3182 trace_initcall_finish_cb 2896 trace_initcall_finish_cb
3183 2897
3184 # cat set_ftrace_filter 2898 # cat set_ftrace_filter
3185 trace_initcall_finish_cb 2899 trace_initcall_finish_cb
3186 2900
3187 # head -50 available_filter_functions | tai 2901 # head -50 available_filter_functions | tail -1
3188 x86_pmu_commit_txn 2902 x86_pmu_commit_txn
3189 2903
3190 # echo 1 50 > set_ftrace_filter 2904 # echo 1 50 > set_ftrace_filter
3191 # cat set_ftrace_filter 2905 # cat set_ftrace_filter
3192 trace_initcall_finish_cb 2906 trace_initcall_finish_cb
3193 x86_pmu_commit_txn 2907 x86_pmu_commit_txn
3194 2908
3195 Dynamic ftrace with the function graph tracer 2909 Dynamic ftrace with the function graph tracer
3196 --------------------------------------------- 2910 ---------------------------------------------
3197 2911
3198 Although what has been explained above concer 2912 Although what has been explained above concerns both the
3199 function tracer and the function-graph-tracer 2913 function tracer and the function-graph-tracer, there are some
3200 special features only available in the functi 2914 special features only available in the function-graph tracer.
3201 2915
3202 If you want to trace only one function and al 2916 If you want to trace only one function and all of its children,
3203 you just have to echo its name into set_graph 2917 you just have to echo its name into set_graph_function::
3204 2918
3205 echo __do_fault > set_graph_function 2919 echo __do_fault > set_graph_function
3206 2920
3207 will produce the following "expanded" trace o 2921 will produce the following "expanded" trace of the __do_fault()
3208 function:: 2922 function::
3209 2923
3210 0) | __do_fault() { 2924 0) | __do_fault() {
3211 0) | filemap_fault() { 2925 0) | filemap_fault() {
3212 0) | find_lock_page() { 2926 0) | find_lock_page() {
3213 0) 0.804 us | find_get_page(); 2927 0) 0.804 us | find_get_page();
3214 0) | __might_sleep() 2928 0) | __might_sleep() {
3215 0) 1.329 us | } 2929 0) 1.329 us | }
3216 0) 3.904 us | } 2930 0) 3.904 us | }
3217 0) 4.979 us | } 2931 0) 4.979 us | }
3218 0) 0.653 us | _spin_lock(); 2932 0) 0.653 us | _spin_lock();
3219 0) 0.578 us | page_add_file_rmap() 2933 0) 0.578 us | page_add_file_rmap();
3220 0) 0.525 us | native_set_pte_at(); 2934 0) 0.525 us | native_set_pte_at();
3221 0) 0.585 us | _spin_unlock(); 2935 0) 0.585 us | _spin_unlock();
3222 0) | unlock_page() { 2936 0) | unlock_page() {
3223 0) 0.541 us | page_waitqueue(); 2937 0) 0.541 us | page_waitqueue();
3224 0) 0.639 us | __wake_up_bit(); 2938 0) 0.639 us | __wake_up_bit();
3225 0) 2.786 us | } 2939 0) 2.786 us | }
3226 0) + 14.237 us | } 2940 0) + 14.237 us | }
3227 0) | __do_fault() { 2941 0) | __do_fault() {
3228 0) | filemap_fault() { 2942 0) | filemap_fault() {
3229 0) | find_lock_page() { 2943 0) | find_lock_page() {
3230 0) 0.698 us | find_get_page(); 2944 0) 0.698 us | find_get_page();
3231 0) | __might_sleep() 2945 0) | __might_sleep() {
3232 0) 1.412 us | } 2946 0) 1.412 us | }
3233 0) 3.950 us | } 2947 0) 3.950 us | }
3234 0) 5.098 us | } 2948 0) 5.098 us | }
3235 0) 0.631 us | _spin_lock(); 2949 0) 0.631 us | _spin_lock();
3236 0) 0.571 us | page_add_file_rmap() 2950 0) 0.571 us | page_add_file_rmap();
3237 0) 0.526 us | native_set_pte_at(); 2951 0) 0.526 us | native_set_pte_at();
3238 0) 0.586 us | _spin_unlock(); 2952 0) 0.586 us | _spin_unlock();
3239 0) | unlock_page() { 2953 0) | unlock_page() {
3240 0) 0.533 us | page_waitqueue(); 2954 0) 0.533 us | page_waitqueue();
3241 0) 0.638 us | __wake_up_bit(); 2955 0) 0.638 us | __wake_up_bit();
3242 0) 2.793 us | } 2956 0) 2.793 us | }
3243 0) + 14.012 us | } 2957 0) + 14.012 us | }
3244 2958
3245 You can also expand several functions at once 2959 You can also expand several functions at once::
3246 2960
3247 echo sys_open > set_graph_function 2961 echo sys_open > set_graph_function
3248 echo sys_close >> set_graph_function 2962 echo sys_close >> set_graph_function
3249 2963
3250 Now if you want to go back to trace all funct 2964 Now if you want to go back to trace all functions you can clear
3251 this special filter via:: 2965 this special filter via::
3252 2966
3253 echo > set_graph_function 2967 echo > set_graph_function
3254 2968
3255 2969
3256 ftrace_enabled 2970 ftrace_enabled
3257 -------------- 2971 --------------
3258 2972
3259 Note, the proc sysctl ftrace_enable is a big 2973 Note, the proc sysctl ftrace_enable is a big on/off switch for the
3260 function tracer. By default it is enabled (wh 2974 function tracer. By default it is enabled (when function tracing is
3261 enabled in the kernel). If it is disabled, al 2975 enabled in the kernel). If it is disabled, all function tracing is
3262 disabled. This includes not only the function 2976 disabled. This includes not only the function tracers for ftrace, but
3263 also for any other uses (perf, kprobes, stack !! 2977 also for any other uses (perf, kprobes, stack tracing, profiling, etc).
3264 cannot be disabled if there is a callback wit <<
3265 registered. <<
3266 2978
3267 Please disable this with care. 2979 Please disable this with care.
3268 2980
3269 This can be disable (and enabled) with:: 2981 This can be disable (and enabled) with::
3270 2982
3271 sysctl kernel.ftrace_enabled=0 2983 sysctl kernel.ftrace_enabled=0
3272 sysctl kernel.ftrace_enabled=1 2984 sysctl kernel.ftrace_enabled=1
3273 2985
3274 or 2986 or
3275 2987
3276 echo 0 > /proc/sys/kernel/ftrace_enabled 2988 echo 0 > /proc/sys/kernel/ftrace_enabled
3277 echo 1 > /proc/sys/kernel/ftrace_enabled 2989 echo 1 > /proc/sys/kernel/ftrace_enabled
3278 2990
3279 2991
3280 Filter commands 2992 Filter commands
3281 --------------- 2993 ---------------
3282 2994
3283 A few commands are supported by the set_ftrac 2995 A few commands are supported by the set_ftrace_filter interface.
3284 Trace commands have the following format:: 2996 Trace commands have the following format::
3285 2997
3286 <function>:<command>:<parameter> 2998 <function>:<command>:<parameter>
3287 2999
3288 The following commands are supported: 3000 The following commands are supported:
3289 3001
3290 - mod: 3002 - mod:
3291 This command enables function filtering per 3003 This command enables function filtering per module. The
3292 parameter defines the module. For example, 3004 parameter defines the module. For example, if only the write*
3293 functions in the ext3 module are desired, r 3005 functions in the ext3 module are desired, run:
3294 3006
3295 echo 'write*:mod:ext3' > set_ftrace_filter 3007 echo 'write*:mod:ext3' > set_ftrace_filter
3296 3008
3297 This command interacts with the filter in t 3009 This command interacts with the filter in the same way as
3298 filtering based on function names. Thus, ad 3010 filtering based on function names. Thus, adding more functions
3299 in a different module is accomplished by ap 3011 in a different module is accomplished by appending (>>) to the
3300 filter file. Remove specific module functio 3012 filter file. Remove specific module functions by prepending
3301 '!':: 3013 '!'::
3302 3014
3303 echo '!writeback*:mod:ext3' >> set_ftrace_ 3015 echo '!writeback*:mod:ext3' >> set_ftrace_filter
3304 3016
3305 Mod command supports module globbing. Disab 3017 Mod command supports module globbing. Disable tracing for all
3306 functions except a specific module:: 3018 functions except a specific module::
3307 3019
3308 echo '!*:mod:!ext3' >> set_ftrace_filter 3020 echo '!*:mod:!ext3' >> set_ftrace_filter
3309 3021
3310 Disable tracing for all modules, but still 3022 Disable tracing for all modules, but still trace kernel::
3311 3023
3312 echo '!*:mod:*' >> set_ftrace_filter 3024 echo '!*:mod:*' >> set_ftrace_filter
3313 3025
3314 Enable filter only for kernel:: 3026 Enable filter only for kernel::
3315 3027
3316 echo '*write*:mod:!*' >> set_ftrace_filter 3028 echo '*write*:mod:!*' >> set_ftrace_filter
3317 3029
3318 Enable filter for module globbing:: 3030 Enable filter for module globbing::
3319 3031
3320 echo '*write*:mod:*snd*' >> set_ftrace_fil 3032 echo '*write*:mod:*snd*' >> set_ftrace_filter
3321 3033
3322 - traceon/traceoff: 3034 - traceon/traceoff:
3323 These commands turn tracing on and off when 3035 These commands turn tracing on and off when the specified
3324 functions are hit. The parameter determines 3036 functions are hit. The parameter determines how many times the
3325 tracing system is turned on and off. If uns 3037 tracing system is turned on and off. If unspecified, there is
3326 no limit. For example, to disable tracing w 3038 no limit. For example, to disable tracing when a schedule bug
3327 is hit the first 5 times, run:: 3039 is hit the first 5 times, run::
3328 3040
3329 echo '__schedule_bug:traceoff:5' > set_ftr 3041 echo '__schedule_bug:traceoff:5' > set_ftrace_filter
3330 3042
3331 To always disable tracing when __schedule_b 3043 To always disable tracing when __schedule_bug is hit::
3332 3044
3333 echo '__schedule_bug:traceoff' > set_ftrac 3045 echo '__schedule_bug:traceoff' > set_ftrace_filter
3334 3046
3335 These commands are cumulative whether or no 3047 These commands are cumulative whether or not they are appended
3336 to set_ftrace_filter. To remove a command, 3048 to set_ftrace_filter. To remove a command, prepend it by '!'
3337 and drop the parameter:: 3049 and drop the parameter::
3338 3050
3339 echo '!__schedule_bug:traceoff:0' > set_ft 3051 echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
3340 3052
3341 The above removes the traceoff command for 3053 The above removes the traceoff command for __schedule_bug
3342 that have a counter. To remove commands wit 3054 that have a counter. To remove commands without counters::
3343 3055
3344 echo '!__schedule_bug:traceoff' > set_ftra 3056 echo '!__schedule_bug:traceoff' > set_ftrace_filter
3345 3057
3346 - snapshot: 3058 - snapshot:
3347 Will cause a snapshot to be triggered when 3059 Will cause a snapshot to be triggered when the function is hit.
3348 :: 3060 ::
3349 3061
3350 echo 'native_flush_tlb_others:snapshot' > 3062 echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
3351 3063
3352 To only snapshot once: 3064 To only snapshot once:
3353 :: 3065 ::
3354 3066
3355 echo 'native_flush_tlb_others:snapshot:1' 3067 echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
3356 3068
3357 To remove the above commands:: 3069 To remove the above commands::
3358 3070
3359 echo '!native_flush_tlb_others:snapshot' > 3071 echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
3360 echo '!native_flush_tlb_others:snapshot:0' 3072 echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
3361 3073
3362 - enable_event/disable_event: 3074 - enable_event/disable_event:
3363 These commands can enable or disable a trac 3075 These commands can enable or disable a trace event. Note, because
3364 function tracing callbacks are very sensiti 3076 function tracing callbacks are very sensitive, when these commands
3365 are registered, the trace point is activate 3077 are registered, the trace point is activated, but disabled in
3366 a "soft" mode. That is, the tracepoint will 3078 a "soft" mode. That is, the tracepoint will be called, but
3367 just will not be traced. The event tracepoi 3079 just will not be traced. The event tracepoint stays in this mode
3368 as long as there's a command that triggers 3080 as long as there's a command that triggers it.
3369 :: 3081 ::
3370 3082
3371 echo 'try_to_wake_up:enable_event:sched:sc 3083 echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
3372 set_ftrace_filter 3084 set_ftrace_filter
3373 3085
3374 The format is:: 3086 The format is::
3375 3087
3376 <function>:enable_event:<system>:<event>[ 3088 <function>:enable_event:<system>:<event>[:count]
3377 <function>:disable_event:<system>:<event> 3089 <function>:disable_event:<system>:<event>[:count]
3378 3090
3379 To remove the events commands:: 3091 To remove the events commands::
3380 3092
3381 echo '!try_to_wake_up:enable_event:sched:s 3093 echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
3382 set_ftrace_filter 3094 set_ftrace_filter
3383 echo '!schedule:disable_event:sched:sched_ 3095 echo '!schedule:disable_event:sched:sched_switch' > \
3384 set_ftrace_filter 3096 set_ftrace_filter
3385 3097
3386 - dump: 3098 - dump:
3387 When the function is hit, it will dump the 3099 When the function is hit, it will dump the contents of the ftrace
3388 ring buffer to the console. This is useful 3100 ring buffer to the console. This is useful if you need to debug
3389 something, and want to dump the trace when 3101 something, and want to dump the trace when a certain function
3390 is hit. Perhaps it's a function that is cal 3102 is hit. Perhaps it's a function that is called before a triple
3391 fault happens and does not allow you to get 3103 fault happens and does not allow you to get a regular dump.
3392 3104
3393 - cpudump: 3105 - cpudump:
3394 When the function is hit, it will dump the 3106 When the function is hit, it will dump the contents of the ftrace
3395 ring buffer for the current CPU to the cons 3107 ring buffer for the current CPU to the console. Unlike the "dump"
3396 command, it only prints out the contents of 3108 command, it only prints out the contents of the ring buffer for the
3397 CPU that executed the function that trigger 3109 CPU that executed the function that triggered the dump.
3398 3110
3399 - stacktrace: 3111 - stacktrace:
3400 When the function is hit, a stack trace is 3112 When the function is hit, a stack trace is recorded.
3401 3113
3402 trace_pipe 3114 trace_pipe
3403 ---------- 3115 ----------
3404 3116
3405 The trace_pipe outputs the same content as th 3117 The trace_pipe outputs the same content as the trace file, but
3406 the effect on the tracing is different. Every 3118 the effect on the tracing is different. Every read from
3407 trace_pipe is consumed. This means that subse 3119 trace_pipe is consumed. This means that subsequent reads will be
3408 different. The trace is live. 3120 different. The trace is live.
3409 :: 3121 ::
3410 3122
3411 # echo function > current_tracer 3123 # echo function > current_tracer
3412 # cat trace_pipe > /tmp/trace.out & 3124 # cat trace_pipe > /tmp/trace.out &
3413 [1] 4153 3125 [1] 4153
3414 # echo 1 > tracing_on 3126 # echo 1 > tracing_on
3415 # usleep 1 3127 # usleep 1
3416 # echo 0 > tracing_on 3128 # echo 0 > tracing_on
3417 # cat trace 3129 # cat trace
3418 # tracer: function 3130 # tracer: function
3419 # 3131 #
3420 # entries-in-buffer/entries-written: 0/0 3132 # entries-in-buffer/entries-written: 0/0 #P:4
3421 # 3133 #
3422 # _-----=> irq 3134 # _-----=> irqs-off
3423 # / _----=> nee 3135 # / _----=> need-resched
3424 # | / _---=> har 3136 # | / _---=> hardirq/softirq
3425 # || / _--=> pre 3137 # || / _--=> preempt-depth
3426 # ||| / dela 3138 # ||| / delay
3427 # TASK-PID CPU# |||| TIMEST 3139 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3428 # | | | |||| | 3140 # | | | |||| | |
3429 3141
3430 # 3142 #
3431 # cat /tmp/trace.out 3143 # cat /tmp/trace.out
3432 bash-1994 [000] .... 5281.5689 3144 bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write
3433 bash-1994 [000] .... 5281.5689 3145 bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock
3434 bash-1994 [000] .... 5281.5689 3146 bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify
3435 bash-1994 [000] .... 5281.5689 3147 bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify
3436 bash-1994 [000] .... 5281.5689 3148 bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify
3437 bash-1994 [000] .... 5281.5689 3149 bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock
3438 bash-1994 [000] ...1 5281.5689 3150 bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock
3439 bash-1994 [000] .... 5281.5689 3151 bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify
3440 bash-1994 [000] .... 5281.5689 3152 bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath
3441 3153
3442 3154
3443 Note, reading the trace_pipe file will block 3155 Note, reading the trace_pipe file will block until more input is
3444 added. This is contrary to the trace file. If !! 3156 added.
3445 the trace file for reading, it will actually <<
3446 prevent new entries from being added. The tra <<
3447 not have this limitation. <<
3448 3157
3449 trace entries 3158 trace entries
3450 ------------- 3159 -------------
3451 3160
3452 Having too much or not enough data can be tro 3161 Having too much or not enough data can be troublesome in
3453 diagnosing an issue in the kernel. The file b 3162 diagnosing an issue in the kernel. The file buffer_size_kb is
3454 used to modify the size of the internal trace 3163 used to modify the size of the internal trace buffers. The
3455 number listed is the number of entries that c 3164 number listed is the number of entries that can be recorded per
3456 CPU. To know the full size, multiply the numb 3165 CPU. To know the full size, multiply the number of possible CPUs
3457 with the number of entries. 3166 with the number of entries.
3458 :: 3167 ::
3459 3168
3460 # cat buffer_size_kb 3169 # cat buffer_size_kb
3461 1408 (units kilobytes) 3170 1408 (units kilobytes)
3462 3171
3463 Or simply read buffer_total_size_kb 3172 Or simply read buffer_total_size_kb
3464 :: 3173 ::
3465 3174
3466 # cat buffer_total_size_kb 3175 # cat buffer_total_size_kb
3467 5632 3176 5632
3468 3177
3469 To modify the buffer, simple echo in a number 3178 To modify the buffer, simple echo in a number (in 1024 byte segments).
3470 :: 3179 ::
3471 3180
3472 # echo 10000 > buffer_size_kb 3181 # echo 10000 > buffer_size_kb
3473 # cat buffer_size_kb 3182 # cat buffer_size_kb
3474 10000 (units kilobytes) 3183 10000 (units kilobytes)
3475 3184
3476 It will try to allocate as much as possible. 3185 It will try to allocate as much as possible. If you allocate too
3477 much, it can cause Out-Of-Memory to trigger. 3186 much, it can cause Out-Of-Memory to trigger.
3478 :: 3187 ::
3479 3188
3480 # echo 1000000000000 > buffer_size_kb 3189 # echo 1000000000000 > buffer_size_kb
3481 -bash: echo: write error: Cannot allocate m 3190 -bash: echo: write error: Cannot allocate memory
3482 # cat buffer_size_kb 3191 # cat buffer_size_kb
3483 85 3192 85
3484 3193
3485 The per_cpu buffers can be changed individual 3194 The per_cpu buffers can be changed individually as well:
3486 :: 3195 ::
3487 3196
3488 # echo 10000 > per_cpu/cpu0/buffer_size_kb 3197 # echo 10000 > per_cpu/cpu0/buffer_size_kb
3489 # echo 100 > per_cpu/cpu1/buffer_size_kb 3198 # echo 100 > per_cpu/cpu1/buffer_size_kb
3490 3199
3491 When the per_cpu buffers are not the same, th 3200 When the per_cpu buffers are not the same, the buffer_size_kb
3492 at the top level will just show an X 3201 at the top level will just show an X
3493 :: 3202 ::
3494 3203
3495 # cat buffer_size_kb 3204 # cat buffer_size_kb
3496 X 3205 X
3497 3206
3498 This is where the buffer_total_size_kb is use 3207 This is where the buffer_total_size_kb is useful:
3499 :: 3208 ::
3500 3209
3501 # cat buffer_total_size_kb 3210 # cat buffer_total_size_kb
3502 12916 3211 12916
3503 3212
3504 Writing to the top level buffer_size_kb will 3213 Writing to the top level buffer_size_kb will reset all the buffers
3505 to be the same again. 3214 to be the same again.
3506 3215
3507 Snapshot 3216 Snapshot
3508 -------- 3217 --------
3509 CONFIG_TRACER_SNAPSHOT makes a generic snapsh 3218 CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
3510 available to all non latency tracers. (Latenc 3219 available to all non latency tracers. (Latency tracers which
3511 record max latency, such as "irqsoff" or "wak 3220 record max latency, such as "irqsoff" or "wakeup", can't use
3512 this feature, since those are already using t 3221 this feature, since those are already using the snapshot
3513 mechanism internally.) 3222 mechanism internally.)
3514 3223
3515 Snapshot preserves a current trace buffer at 3224 Snapshot preserves a current trace buffer at a particular point
3516 in time without stopping tracing. Ftrace swap 3225 in time without stopping tracing. Ftrace swaps the current
3517 buffer with a spare buffer, and tracing conti 3226 buffer with a spare buffer, and tracing continues in the new
3518 current (=previous spare) buffer. 3227 current (=previous spare) buffer.
3519 3228
3520 The following tracefs files in "tracing" are 3229 The following tracefs files in "tracing" are related to this
3521 feature: 3230 feature:
3522 3231
3523 snapshot: 3232 snapshot:
3524 3233
3525 This is used to take a snapshot and t 3234 This is used to take a snapshot and to read the output
3526 of the snapshot. Echo 1 into this fil 3235 of the snapshot. Echo 1 into this file to allocate a
3527 spare buffer and to take a snapshot ( 3236 spare buffer and to take a snapshot (swap), then read
3528 the snapshot from this file in the sa 3237 the snapshot from this file in the same format as
3529 "trace" (described above in the secti 3238 "trace" (described above in the section "The File
3530 System"). Both reads snapshot and tra 3239 System"). Both reads snapshot and tracing are executable
3531 in parallel. When the spare buffer is 3240 in parallel. When the spare buffer is allocated, echoing
3532 0 frees it, and echoing else (positiv 3241 0 frees it, and echoing else (positive) values clear the
3533 snapshot contents. 3242 snapshot contents.
3534 More details are shown in the table b 3243 More details are shown in the table below.
3535 3244
3536 +--------------+------------+-------- 3245 +--------------+------------+------------+------------+
3537 |status\\input | 0 | 1 3246 |status\\input | 0 | 1 | else |
3538 +==============+============+======== 3247 +==============+============+============+============+
3539 |not allocated |(do nothing)| alloc+s 3248 |not allocated |(do nothing)| alloc+swap |(do nothing)|
3540 +--------------+------------+-------- 3249 +--------------+------------+------------+------------+
3541 |allocated | free | swap 3250 |allocated | free | swap | clear |
3542 +--------------+------------+-------- 3251 +--------------+------------+------------+------------+
3543 3252
3544 Here is an example of using the snapshot feat 3253 Here is an example of using the snapshot feature.
3545 :: 3254 ::
3546 3255
3547 # echo 1 > events/sched/enable 3256 # echo 1 > events/sched/enable
3548 # echo 1 > snapshot 3257 # echo 1 > snapshot
3549 # cat snapshot 3258 # cat snapshot
3550 # tracer: nop 3259 # tracer: nop
3551 # 3260 #
3552 # entries-in-buffer/entries-written: 71/71 3261 # entries-in-buffer/entries-written: 71/71 #P:8
3553 # 3262 #
3554 # _-----=> irq 3263 # _-----=> irqs-off
3555 # / _----=> nee 3264 # / _----=> need-resched
3556 # | / _---=> har 3265 # | / _---=> hardirq/softirq
3557 # || / _--=> pre 3266 # || / _--=> preempt-depth
3558 # ||| / dela 3267 # ||| / delay
3559 # TASK-PID CPU# |||| TIMEST 3268 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3560 # | | | |||| | 3269 # | | | |||| | |
3561 <idle>-0 [005] d... 2440.603 3270 <idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
3562 sleep-2242 [005] d... 2440.603 3271 sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
3563 [...] 3272 [...]
3564 <idle>-0 [002] d... 2440.70723 3273 <idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
3565 3274
3566 # cat trace 3275 # cat trace
3567 # tracer: nop 3276 # tracer: nop
3568 # 3277 #
3569 # entries-in-buffer/entries-written: 77/77 3278 # entries-in-buffer/entries-written: 77/77 #P:8
3570 # 3279 #
3571 # _-----=> irq 3280 # _-----=> irqs-off
3572 # / _----=> nee 3281 # / _----=> need-resched
3573 # | / _---=> har 3282 # | / _---=> hardirq/softirq
3574 # || / _--=> pre 3283 # || / _--=> preempt-depth
3575 # ||| / dela 3284 # ||| / delay
3576 # TASK-PID CPU# |||| TIMEST 3285 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3577 # | | | |||| | 3286 # | | | |||| | |
3578 <idle>-0 [007] d... 2440.707 3287 <idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
3579 snapshot-test-2-2229 [002] d... 2440.707 3288 snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
3580 [...] 3289 [...]
3581 3290
3582 3291
3583 If you try to use this snapshot feature when 3292 If you try to use this snapshot feature when current tracer is
3584 one of the latency tracers, you will get the 3293 one of the latency tracers, you will get the following results.
3585 :: 3294 ::
3586 3295
3587 # echo wakeup > current_tracer 3296 # echo wakeup > current_tracer
3588 # echo 1 > snapshot 3297 # echo 1 > snapshot
3589 bash: echo: write error: Device or resource 3298 bash: echo: write error: Device or resource busy
3590 # cat snapshot 3299 # cat snapshot
3591 cat: snapshot: Device or resource busy 3300 cat: snapshot: Device or resource busy
3592 3301
3593 3302
3594 Instances 3303 Instances
3595 --------- 3304 ---------
3596 In the tracefs tracing directory, there is a !! 3305 In the tracefs tracing directory is a directory called "instances".
3597 This directory can have new directories creat 3306 This directory can have new directories created inside of it using
3598 mkdir, and removing directories with rmdir. T 3307 mkdir, and removing directories with rmdir. The directory created
3599 with mkdir in this directory will already con 3308 with mkdir in this directory will already contain files and other
3600 directories after it is created. 3309 directories after it is created.
3601 :: 3310 ::
3602 3311
3603 # mkdir instances/foo 3312 # mkdir instances/foo
3604 # ls instances/foo 3313 # ls instances/foo
3605 buffer_size_kb buffer_total_size_kb event 3314 buffer_size_kb buffer_total_size_kb events free_buffer per_cpu
3606 set_event snapshot trace trace_clock tr 3315 set_event snapshot trace trace_clock trace_marker trace_options
3607 trace_pipe tracing_on 3316 trace_pipe tracing_on
3608 3317
3609 As you can see, the new directory looks simil 3318 As you can see, the new directory looks similar to the tracing directory
3610 itself. In fact, it is very similar, except t 3319 itself. In fact, it is very similar, except that the buffer and
3611 events are agnostic from the main directory, !! 3320 events are agnostic from the main director, or from any other
3612 instances that are created. 3321 instances that are created.
3613 3322
3614 The files in the new directory work just like 3323 The files in the new directory work just like the files with the
3615 same name in the tracing directory except the 3324 same name in the tracing directory except the buffer that is used
3616 is a separate and new buffer. The files affec 3325 is a separate and new buffer. The files affect that buffer but do not
3617 affect the main buffer with the exception of 3326 affect the main buffer with the exception of trace_options. Currently,
3618 the trace_options affect all instances and th 3327 the trace_options affect all instances and the top level buffer
3619 the same, but this may change in future relea 3328 the same, but this may change in future releases. That is, options
3620 may become specific to the instance they resi 3329 may become specific to the instance they reside in.
3621 3330
3622 Notice that none of the function tracer files 3331 Notice that none of the function tracer files are there, nor is
3623 current_tracer and available_tracers. This is 3332 current_tracer and available_tracers. This is because the buffers
3624 can currently only have events enabled for th 3333 can currently only have events enabled for them.
3625 :: 3334 ::
3626 3335
3627 # mkdir instances/foo 3336 # mkdir instances/foo
3628 # mkdir instances/bar 3337 # mkdir instances/bar
3629 # mkdir instances/zoot 3338 # mkdir instances/zoot
3630 # echo 100000 > buffer_size_kb 3339 # echo 100000 > buffer_size_kb
3631 # echo 1000 > instances/foo/buffer_size_kb 3340 # echo 1000 > instances/foo/buffer_size_kb
3632 # echo 5000 > instances/bar/per_cpu/cpu1/bu 3341 # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
3633 # echo function > current_trace 3342 # echo function > current_trace
3634 # echo 1 > instances/foo/events/sched/sched 3343 # echo 1 > instances/foo/events/sched/sched_wakeup/enable
3635 # echo 1 > instances/foo/events/sched/sched 3344 # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
3636 # echo 1 > instances/foo/events/sched/sched 3345 # echo 1 > instances/foo/events/sched/sched_switch/enable
3637 # echo 1 > instances/bar/events/irq/enable 3346 # echo 1 > instances/bar/events/irq/enable
3638 # echo 1 > instances/zoot/events/syscalls/e 3347 # echo 1 > instances/zoot/events/syscalls/enable
3639 # cat trace_pipe 3348 # cat trace_pipe
3640 CPU:2 [LOST 11745 EVENTS] 3349 CPU:2 [LOST 11745 EVENTS]
3641 bash-2044 [002] .... 10594.481 3350 bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
3642 bash-2044 [002] d... 10594.481 3351 bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
3643 bash-2044 [002] d..1 10594.481 3352 bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
3644 bash-2044 [002] d..1 10594.481 3353 bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
3645 bash-2044 [002] d..1 10594.481 3354 bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
3646 bash-2044 [002] d... 10594.481 3355 bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
3647 bash-2044 [002] d... 10594.481 3356 bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
3648 bash-2044 [002] d... 10594.481 3357 bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
3649 bash-2044 [002] d... 10594.481 3358 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
3650 bash-2044 [002] d... 10594.481 3359 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
3651 bash-2044 [002] .... 10594.481 3360 bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process
3652 [...] 3361 [...]
3653 3362
3654 # cat instances/foo/trace_pipe 3363 # cat instances/foo/trace_pipe
3655 bash-1998 [000] d..4 136.676 3364 bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
3656 bash-1998 [000] dN.4 136.676 3365 bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
3657 <idle>-0 [003] d.h3 136.676 3366 <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
3658 <idle>-0 [003] d..3 136.676 3367 <idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120
3659 rcu_preempt-9 [003] d..3 136.676 3368 rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120
3660 bash-1998 [000] d..4 136.677 3369 bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
3661 bash-1998 [000] dN.4 136.677 3370 bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
3662 bash-1998 [000] d..3 136.677 3371 bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120
3663 kworker/0:1-59 [000] d..4 136.677 3372 kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
3664 kworker/0:1-59 [000] d..3 136.677 3373 kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120
3665 [...] 3374 [...]
3666 3375
3667 # cat instances/bar/trace_pipe 3376 # cat instances/bar/trace_pipe
3668 migration/1-14 [001] d.h3 138.732 3377 migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX]
3669 <idle>-0 [001] dNh3 138.732 3378 <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX]
3670 bash-1998 [000] d.h1 138.733 3379 bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER]
3671 bash-1998 [000] d.h1 138.733 3380 bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU]
3672 bash-1998 [000] ..s2 138.733 3381 bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER]
3673 bash-1998 [000] ..s2 138.733 3382 bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER]
3674 bash-1998 [000] ..s2 138.733 3383 bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU]
3675 bash-1998 [000] ..s2 138.733 3384 bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU]
3676 sshd-1995 [001] d.h1 138.733 3385 sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
3677 sshd-1995 [001] d.h1 138.733 3386 sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled
3678 sshd-1995 [001] d.h1 138.733 3387 sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0
3679 sshd-1995 [001] d.h1 138.733 3388 sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled
3680 [...] 3389 [...]
3681 3390
3682 # cat instances/zoot/trace 3391 # cat instances/zoot/trace
3683 # tracer: nop 3392 # tracer: nop
3684 # 3393 #
3685 # entries-in-buffer/entries-written: 18996/ 3394 # entries-in-buffer/entries-written: 18996/18996 #P:4
3686 # 3395 #
3687 # _-----=> irq 3396 # _-----=> irqs-off
3688 # / _----=> nee 3397 # / _----=> need-resched
3689 # | / _---=> har 3398 # | / _---=> hardirq/softirq
3690 # || / _--=> pre 3399 # || / _--=> preempt-depth
3691 # ||| / dela 3400 # ||| / delay
3692 # TASK-PID CPU# |||| TIMEST 3401 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
3693 # | | | |||| | 3402 # | | | |||| | |
3694 bash-1998 [000] d... 140.733 3403 bash-1998 [000] d... 140.733501: sys_write -> 0x2
3695 bash-1998 [000] d... 140.733 3404 bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1)
3696 bash-1998 [000] d... 140.733 3405 bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1
3697 bash-1998 [000] d... 140.733 3406 bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
3698 bash-1998 [000] d... 140.733 3407 bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1
3699 bash-1998 [000] d... 140.733 3408 bash-1998 [000] d... 140.733510: sys_close(fd: a)
3700 bash-1998 [000] d... 140.733 3409 bash-1998 [000] d... 140.733510: sys_close -> 0x0
3701 bash-1998 [000] d... 140.733 3410 bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
3702 bash-1998 [000] d... 140.733 3411 bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0
3703 bash-1998 [000] d... 140.733 3412 bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
3704 bash-1998 [000] d... 140.733 3413 bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0
3705 3414
3706 You can see that the trace of the top most tr 3415 You can see that the trace of the top most trace buffer shows only
3707 the function tracing. The foo instance displa 3416 the function tracing. The foo instance displays wakeups and task
3708 switches. 3417 switches.
3709 3418
3710 To remove the instances, simply delete their 3419 To remove the instances, simply delete their directories:
3711 :: 3420 ::
3712 3421
3713 # rmdir instances/foo 3422 # rmdir instances/foo
3714 # rmdir instances/bar 3423 # rmdir instances/bar
3715 # rmdir instances/zoot 3424 # rmdir instances/zoot
3716 3425
3717 Note, if a process has a trace file open in o 3426 Note, if a process has a trace file open in one of the instance
3718 directories, the rmdir will fail with EBUSY. 3427 directories, the rmdir will fail with EBUSY.
3719 3428
3720 3429
3721 Stack trace 3430 Stack trace
3722 ----------- 3431 -----------
3723 Since the kernel has a fixed sized stack, it 3432 Since the kernel has a fixed sized stack, it is important not to
3724 waste it in functions. A kernel developer mus !! 3433 waste it in functions. A kernel developer must be conscience of
3725 what they allocate on the stack. If they add 3434 what they allocate on the stack. If they add too much, the system
3726 can be in danger of a stack overflow, and cor 3435 can be in danger of a stack overflow, and corruption will occur,
3727 usually leading to a system panic. 3436 usually leading to a system panic.
3728 3437
3729 There are some tools that check this, usually 3438 There are some tools that check this, usually with interrupts
3730 periodically checking usage. But if you can p 3439 periodically checking usage. But if you can perform a check
3731 at every function call that will become very 3440 at every function call that will become very useful. As ftrace provides
3732 a function tracer, it makes it convenient to 3441 a function tracer, it makes it convenient to check the stack size
3733 at every function call. This is enabled via t 3442 at every function call. This is enabled via the stack tracer.
3734 3443
3735 CONFIG_STACK_TRACER enables the ftrace stack 3444 CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
3736 To enable it, write a '1' into /proc/sys/kern 3445 To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
3737 :: 3446 ::
3738 3447
3739 # echo 1 > /proc/sys/kernel/stack_tracer_ena 3448 # echo 1 > /proc/sys/kernel/stack_tracer_enabled
3740 3449
3741 You can also enable it from the kernel comman 3450 You can also enable it from the kernel command line to trace
3742 the stack size of the kernel during boot up, 3451 the stack size of the kernel during boot up, by adding "stacktrace"
3743 to the kernel command line parameter. 3452 to the kernel command line parameter.
3744 3453
3745 After running it for a few minutes, the outpu 3454 After running it for a few minutes, the output looks like:
3746 :: 3455 ::
3747 3456
3748 # cat stack_max_size 3457 # cat stack_max_size
3749 2928 3458 2928
3750 3459
3751 # cat stack_trace 3460 # cat stack_trace
3752 Depth Size Location (18 ent 3461 Depth Size Location (18 entries)
3753 ----- ---- -------- 3462 ----- ---- --------
3754 0) 2928 224 update_sd_lb_stats+ 3463 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac
3755 1) 2704 160 find_busiest_group+ 3464 1) 2704 160 find_busiest_group+0x31/0x1f1
3756 2) 2544 256 load_balance+0xd9/0 3465 2) 2544 256 load_balance+0xd9/0x662
3757 3) 2288 80 idle_balance+0xbb/0 3466 3) 2288 80 idle_balance+0xbb/0x130
3758 4) 2208 128 __schedule+0x26e/0x 3467 4) 2208 128 __schedule+0x26e/0x5b9
3759 5) 2080 16 schedule+0x64/0x66 3468 5) 2080 16 schedule+0x64/0x66
3760 6) 2064 128 schedule_timeout+0x 3469 6) 2064 128 schedule_timeout+0x34/0xe0
3761 7) 1936 112 wait_for_common+0x9 3470 7) 1936 112 wait_for_common+0x97/0xf1
3762 8) 1824 16 wait_for_completion 3471 8) 1824 16 wait_for_completion+0x1d/0x1f
3763 9) 1808 128 flush_work+0xfe/0x1 3472 9) 1808 128 flush_work+0xfe/0x119
3764 10) 1680 16 tty_flush_to_ldisc+ 3473 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20
3765 11) 1664 48 input_available_p+0 3474 11) 1664 48 input_available_p+0x1d/0x5c
3766 12) 1616 48 n_tty_poll+0x6d/0x1 3475 12) 1616 48 n_tty_poll+0x6d/0x134
3767 13) 1568 64 tty_poll+0x64/0x7f 3476 13) 1568 64 tty_poll+0x64/0x7f
3768 14) 1504 880 do_select+0x31e/0x5 3477 14) 1504 880 do_select+0x31e/0x511
3769 15) 624 400 core_sys_select+0x1 3478 15) 624 400 core_sys_select+0x177/0x216
3770 16) 224 96 sys_select+0x91/0xb 3479 16) 224 96 sys_select+0x91/0xb9
3771 17) 128 128 system_call_fastpat 3480 17) 128 128 system_call_fastpath+0x16/0x1b
3772 3481
3773 Note, if -mfentry is being used by gcc, funct 3482 Note, if -mfentry is being used by gcc, functions get traced before
3774 they set up the stack frame. This means that 3483 they set up the stack frame. This means that leaf level functions
3775 are not tested by the stack tracer when -mfen 3484 are not tested by the stack tracer when -mfentry is used.
3776 3485
3777 Currently, -mfentry is used by gcc 4.6.0 and 3486 Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
3778 3487
3779 More 3488 More
3780 ---- 3489 ----
3781 More details can be found in the source code, 3490 More details can be found in the source code, in the `kernel/trace/*.c` files.
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