1 // SPDX-License-Identifier: GPL-2.0-only 1 // SPDX-License-Identifier: GPL-2.0-only
2 /* 2 /*
3 * latencytop.c: Latency display infrastructur 3 * latencytop.c: Latency display infrastructure
4 * 4 *
5 * (C) Copyright 2008 Intel Corporation 5 * (C) Copyright 2008 Intel Corporation
6 * Author: Arjan van de Ven <arjan@linux.intel 6 * Author: Arjan van de Ven <arjan@linux.intel.com>
7 */ 7 */
8 8
9 /* 9 /*
10 * CONFIG_LATENCYTOP enables a kernel latency 10 * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
11 * used by the "latencytop" userspace tool. Th 11 * used by the "latencytop" userspace tool. The latency that is tracked is not
12 * the 'traditional' interrupt latency (which 12 * the 'traditional' interrupt latency (which is primarily caused by something
13 * else consuming CPU), but instead, it is the 13 * else consuming CPU), but instead, it is the latency an application encounters
14 * because the kernel sleeps on its behalf for 14 * because the kernel sleeps on its behalf for various reasons.
15 * 15 *
16 * This code tracks 2 levels of statistics: 16 * This code tracks 2 levels of statistics:
17 * 1) System level latency 17 * 1) System level latency
18 * 2) Per process latency 18 * 2) Per process latency
19 * 19 *
20 * The latency is stored in fixed sized data s 20 * The latency is stored in fixed sized data structures in an accumulated form;
21 * if the "same" latency cause is hit twice, t 21 * if the "same" latency cause is hit twice, this will be tracked as one entry
22 * in the data structure. Both the count, tota 22 * in the data structure. Both the count, total accumulated latency and maximum
23 * latency are tracked in this data structure. 23 * latency are tracked in this data structure. When the fixed size structure is
24 * full, no new causes are tracked until the b 24 * full, no new causes are tracked until the buffer is flushed by writing to
25 * the /proc file; the userspace tool does thi 25 * the /proc file; the userspace tool does this on a regular basis.
26 * 26 *
27 * A latency cause is identified by a stringif 27 * A latency cause is identified by a stringified backtrace at the point that
28 * the scheduler gets invoked. The userland to 28 * the scheduler gets invoked. The userland tool will use this string to
29 * identify the cause of the latency in human 29 * identify the cause of the latency in human readable form.
30 * 30 *
31 * The information is exported via /proc/laten 31 * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
32 * These files look like this: 32 * These files look like this:
33 * 33 *
34 * Latency Top version : v0.1 34 * Latency Top version : v0.1
35 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_i 35 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
36 * | | | | 36 * | | | |
37 * | | | +----> the stringified backt 37 * | | | +----> the stringified backtrace
38 * | | +---------> The maximum latency f 38 * | | +---------> The maximum latency for this entry in microseconds
39 * | +--------------> The accumulated laten 39 * | +--------------> The accumulated latency for this entry (microseconds)
40 * +-------------------> The number of times t 40 * +-------------------> The number of times this entry is hit
41 * 41 *
42 * (note: the average latency is the accumulat 42 * (note: the average latency is the accumulated latency divided by the number
43 * of times) 43 * of times)
44 */ 44 */
45 45
46 #include <linux/kallsyms.h> 46 #include <linux/kallsyms.h>
47 #include <linux/seq_file.h> 47 #include <linux/seq_file.h>
48 #include <linux/notifier.h> 48 #include <linux/notifier.h>
49 #include <linux/spinlock.h> 49 #include <linux/spinlock.h>
50 #include <linux/proc_fs.h> 50 #include <linux/proc_fs.h>
51 #include <linux/latencytop.h> 51 #include <linux/latencytop.h>
52 #include <linux/export.h> 52 #include <linux/export.h>
53 #include <linux/sched.h> 53 #include <linux/sched.h>
54 #include <linux/sched/debug.h> 54 #include <linux/sched/debug.h>
55 #include <linux/sched/stat.h> 55 #include <linux/sched/stat.h>
56 #include <linux/list.h> 56 #include <linux/list.h>
57 #include <linux/stacktrace.h> 57 #include <linux/stacktrace.h>
58 #include <linux/sysctl.h> <<
59 58
60 static DEFINE_RAW_SPINLOCK(latency_lock); 59 static DEFINE_RAW_SPINLOCK(latency_lock);
61 60
62 #define MAXLR 128 61 #define MAXLR 128
63 static struct latency_record latency_record[MA 62 static struct latency_record latency_record[MAXLR];
64 63
65 int latencytop_enabled; 64 int latencytop_enabled;
66 65
67 #ifdef CONFIG_SYSCTL <<
68 static int sysctl_latencytop(const struct ctl_ <<
69 size_t *lenp, loff_t *ppos) <<
70 { <<
71 int err; <<
72 <<
73 err = proc_dointvec(table, write, buff <<
74 if (latencytop_enabled) <<
75 force_schedstat_enabled(); <<
76 <<
77 return err; <<
78 } <<
79 <<
80 static struct ctl_table latencytop_sysctl[] = <<
81 { <<
82 .procname = "latencytop", <<
83 .data = &latencytop_enab <<
84 .maxlen = sizeof(int), <<
85 .mode = 0644, <<
86 .proc_handler = sysctl_laten <<
87 }, <<
88 }; <<
89 #endif <<
90 <<
91 void clear_tsk_latency_tracing(struct task_str 66 void clear_tsk_latency_tracing(struct task_struct *p)
92 { 67 {
93 unsigned long flags; 68 unsigned long flags;
94 69
95 raw_spin_lock_irqsave(&latency_lock, f 70 raw_spin_lock_irqsave(&latency_lock, flags);
96 memset(&p->latency_record, 0, sizeof(p 71 memset(&p->latency_record, 0, sizeof(p->latency_record));
97 p->latency_record_count = 0; 72 p->latency_record_count = 0;
98 raw_spin_unlock_irqrestore(&latency_lo 73 raw_spin_unlock_irqrestore(&latency_lock, flags);
99 } 74 }
100 75
101 static void clear_global_latency_tracing(void) 76 static void clear_global_latency_tracing(void)
102 { 77 {
103 unsigned long flags; 78 unsigned long flags;
104 79
105 raw_spin_lock_irqsave(&latency_lock, f 80 raw_spin_lock_irqsave(&latency_lock, flags);
106 memset(&latency_record, 0, sizeof(late 81 memset(&latency_record, 0, sizeof(latency_record));
107 raw_spin_unlock_irqrestore(&latency_lo 82 raw_spin_unlock_irqrestore(&latency_lock, flags);
108 } 83 }
109 84
110 static void __sched 85 static void __sched
111 account_global_scheduler_latency(struct task_s 86 account_global_scheduler_latency(struct task_struct *tsk,
112 struct latenc 87 struct latency_record *lat)
113 { 88 {
114 int firstnonnull = MAXLR; !! 89 int firstnonnull = MAXLR + 1;
115 int i; 90 int i;
116 91
117 /* skip kernel threads for now */ 92 /* skip kernel threads for now */
118 if (!tsk->mm) 93 if (!tsk->mm)
119 return; 94 return;
120 95
121 for (i = 0; i < MAXLR; i++) { 96 for (i = 0; i < MAXLR; i++) {
122 int q, same = 1; 97 int q, same = 1;
123 98
124 /* Nothing stored: */ 99 /* Nothing stored: */
125 if (!latency_record[i].backtra 100 if (!latency_record[i].backtrace[0]) {
126 if (firstnonnull > i) 101 if (firstnonnull > i)
127 firstnonnull = 102 firstnonnull = i;
128 continue; 103 continue;
129 } 104 }
130 for (q = 0; q < LT_BACKTRACEDE 105 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
131 unsigned long record = 106 unsigned long record = lat->backtrace[q];
132 107
133 if (latency_record[i]. 108 if (latency_record[i].backtrace[q] != record) {
134 same = 0; 109 same = 0;
135 break; 110 break;
136 } 111 }
137 112
138 /* 0 entry marks end o 113 /* 0 entry marks end of backtrace: */
139 if (!record) 114 if (!record)
140 break; 115 break;
141 } 116 }
142 if (same) { 117 if (same) {
143 latency_record[i].coun 118 latency_record[i].count++;
144 latency_record[i].time 119 latency_record[i].time += lat->time;
145 if (lat->time > latenc 120 if (lat->time > latency_record[i].max)
146 latency_record 121 latency_record[i].max = lat->time;
147 return; 122 return;
148 } 123 }
149 } 124 }
150 125
151 i = firstnonnull; 126 i = firstnonnull;
152 if (i >= MAXLR) !! 127 if (i >= MAXLR - 1)
153 return; 128 return;
154 129
155 /* Allocted a new one: */ 130 /* Allocted a new one: */
156 memcpy(&latency_record[i], lat, sizeof 131 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
157 } 132 }
158 133
159 /** 134 /**
160 * __account_scheduler_latency - record an occ 135 * __account_scheduler_latency - record an occurred latency
161 * @tsk - the task struct of the task hitting 136 * @tsk - the task struct of the task hitting the latency
162 * @usecs - the duration of the latency in mic 137 * @usecs - the duration of the latency in microseconds
163 * @inter - 1 if the sleep was interruptible, 138 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
164 * 139 *
165 * This function is the main entry point for r 140 * This function is the main entry point for recording latency entries
166 * as called by the scheduler. 141 * as called by the scheduler.
167 * 142 *
168 * This function has a few special cases to de 143 * This function has a few special cases to deal with normal 'non-latency'
169 * sleeps: specifically, interruptible sleep l 144 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
170 * since this usually is caused by waiting for 145 * since this usually is caused by waiting for events via select() and co.
171 * 146 *
172 * Negative latencies (caused by time going ba 147 * Negative latencies (caused by time going backwards) are also explicitly
173 * skipped. 148 * skipped.
174 */ 149 */
175 void __sched 150 void __sched
176 __account_scheduler_latency(struct task_struct 151 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
177 { 152 {
178 unsigned long flags; 153 unsigned long flags;
179 int i, q; 154 int i, q;
180 struct latency_record lat; 155 struct latency_record lat;
181 156
182 /* Long interruptible waits are genera 157 /* Long interruptible waits are generally user requested... */
183 if (inter && usecs > 5000) 158 if (inter && usecs > 5000)
184 return; 159 return;
185 160
186 /* Negative sleeps are time going back 161 /* Negative sleeps are time going backwards */
187 /* Zero-time sleeps are non-interestin 162 /* Zero-time sleeps are non-interesting */
188 if (usecs <= 0) 163 if (usecs <= 0)
189 return; 164 return;
190 165
191 memset(&lat, 0, sizeof(lat)); 166 memset(&lat, 0, sizeof(lat));
192 lat.count = 1; 167 lat.count = 1;
193 lat.time = usecs; 168 lat.time = usecs;
194 lat.max = usecs; 169 lat.max = usecs;
195 170
196 stack_trace_save_tsk(tsk, lat.backtrac 171 stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0);
197 172
198 raw_spin_lock_irqsave(&latency_lock, f 173 raw_spin_lock_irqsave(&latency_lock, flags);
199 174
200 account_global_scheduler_latency(tsk, 175 account_global_scheduler_latency(tsk, &lat);
201 176
202 for (i = 0; i < tsk->latency_record_co 177 for (i = 0; i < tsk->latency_record_count; i++) {
203 struct latency_record *mylat; 178 struct latency_record *mylat;
204 int same = 1; 179 int same = 1;
205 180
206 mylat = &tsk->latency_record[i 181 mylat = &tsk->latency_record[i];
207 for (q = 0; q < LT_BACKTRACEDE 182 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
208 unsigned long record = 183 unsigned long record = lat.backtrace[q];
209 184
210 if (mylat->backtrace[q 185 if (mylat->backtrace[q] != record) {
211 same = 0; 186 same = 0;
212 break; 187 break;
213 } 188 }
214 189
215 /* 0 entry is end of b 190 /* 0 entry is end of backtrace */
216 if (!record) 191 if (!record)
217 break; 192 break;
218 } 193 }
219 if (same) { 194 if (same) {
220 mylat->count++; 195 mylat->count++;
221 mylat->time += lat.tim 196 mylat->time += lat.time;
222 if (lat.time > mylat-> 197 if (lat.time > mylat->max)
223 mylat->max = l 198 mylat->max = lat.time;
224 goto out_unlock; 199 goto out_unlock;
225 } 200 }
226 } 201 }
227 202
228 /* 203 /*
229 * short term hack; if we're > 32 we s 204 * short term hack; if we're > 32 we stop; future we recycle:
230 */ 205 */
231 if (tsk->latency_record_count >= LT_SA 206 if (tsk->latency_record_count >= LT_SAVECOUNT)
232 goto out_unlock; 207 goto out_unlock;
233 208
234 /* Allocated a new one: */ 209 /* Allocated a new one: */
235 i = tsk->latency_record_count++; 210 i = tsk->latency_record_count++;
236 memcpy(&tsk->latency_record[i], &lat, 211 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
237 212
238 out_unlock: 213 out_unlock:
239 raw_spin_unlock_irqrestore(&latency_lo 214 raw_spin_unlock_irqrestore(&latency_lock, flags);
240 } 215 }
241 216
242 static int lstats_show(struct seq_file *m, voi 217 static int lstats_show(struct seq_file *m, void *v)
243 { 218 {
244 int i; 219 int i;
245 220
246 seq_puts(m, "Latency Top version : v0. 221 seq_puts(m, "Latency Top version : v0.1\n");
247 222
248 for (i = 0; i < MAXLR; i++) { 223 for (i = 0; i < MAXLR; i++) {
249 struct latency_record *lr = &l 224 struct latency_record *lr = &latency_record[i];
250 225
251 if (lr->backtrace[0]) { 226 if (lr->backtrace[0]) {
252 int q; 227 int q;
253 seq_printf(m, "%i %lu 228 seq_printf(m, "%i %lu %lu",
254 lr->count, 229 lr->count, lr->time, lr->max);
255 for (q = 0; q < LT_BAC 230 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
256 unsigned long 231 unsigned long bt = lr->backtrace[q];
257 232
258 if (!bt) 233 if (!bt)
259 break; 234 break;
260 235
261 seq_printf(m, 236 seq_printf(m, " %ps", (void *)bt);
262 } 237 }
263 seq_puts(m, "\n"); 238 seq_puts(m, "\n");
264 } 239 }
265 } 240 }
266 return 0; 241 return 0;
267 } 242 }
268 243
269 static ssize_t 244 static ssize_t
270 lstats_write(struct file *file, const char __u 245 lstats_write(struct file *file, const char __user *buf, size_t count,
271 loff_t *offs) 246 loff_t *offs)
272 { 247 {
273 clear_global_latency_tracing(); 248 clear_global_latency_tracing();
274 249
275 return count; 250 return count;
276 } 251 }
277 252
278 static int lstats_open(struct inode *inode, st 253 static int lstats_open(struct inode *inode, struct file *filp)
279 { 254 {
280 return single_open(filp, lstats_show, 255 return single_open(filp, lstats_show, NULL);
281 } 256 }
282 257
283 static const struct proc_ops lstats_proc_ops = 258 static const struct proc_ops lstats_proc_ops = {
284 .proc_open = lstats_open, 259 .proc_open = lstats_open,
285 .proc_read = seq_read, 260 .proc_read = seq_read,
286 .proc_write = lstats_write, 261 .proc_write = lstats_write,
287 .proc_lseek = seq_lseek, 262 .proc_lseek = seq_lseek,
288 .proc_release = single_release, 263 .proc_release = single_release,
289 }; 264 };
290 265
291 static int __init init_lstats_procfs(void) 266 static int __init init_lstats_procfs(void)
292 { 267 {
293 proc_create("latency_stats", 0644, NUL 268 proc_create("latency_stats", 0644, NULL, &lstats_proc_ops);
294 #ifdef CONFIG_SYSCTL <<
295 register_sysctl_init("kernel", latency <<
296 #endif <<
297 return 0; 269 return 0;
>> 270 }
>> 271
>> 272 int sysctl_latencytop(struct ctl_table *table, int write, void *buffer,
>> 273 size_t *lenp, loff_t *ppos)
>> 274 {
>> 275 int err;
>> 276
>> 277 err = proc_dointvec(table, write, buffer, lenp, ppos);
>> 278 if (latencytop_enabled)
>> 279 force_schedstat_enabled();
>> 280
>> 281 return err;
298 } 282 }
299 device_initcall(init_lstats_procfs); 283 device_initcall(init_lstats_procfs);
300 284
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