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> 58 #include <linux/sysctl.h>
59 59
60 static DEFINE_RAW_SPINLOCK(latency_lock); 60 static DEFINE_RAW_SPINLOCK(latency_lock);
61 61
62 #define MAXLR 128 62 #define MAXLR 128
63 static struct latency_record latency_record[MA 63 static struct latency_record latency_record[MAXLR];
64 64
65 int latencytop_enabled; 65 int latencytop_enabled;
66 66
67 #ifdef CONFIG_SYSCTL 67 #ifdef CONFIG_SYSCTL
68 static int sysctl_latencytop(const struct ctl_ !! 68 static int sysctl_latencytop(struct ctl_table *table, int write, void *buffer,
69 size_t *lenp, loff_t *ppos) 69 size_t *lenp, loff_t *ppos)
70 { 70 {
71 int err; 71 int err;
72 72
73 err = proc_dointvec(table, write, buff 73 err = proc_dointvec(table, write, buffer, lenp, ppos);
74 if (latencytop_enabled) 74 if (latencytop_enabled)
75 force_schedstat_enabled(); 75 force_schedstat_enabled();
76 76
77 return err; 77 return err;
78 } 78 }
79 79
80 static struct ctl_table latencytop_sysctl[] = 80 static struct ctl_table latencytop_sysctl[] = {
81 { 81 {
82 .procname = "latencytop", 82 .procname = "latencytop",
83 .data = &latencytop_enab 83 .data = &latencytop_enabled,
84 .maxlen = sizeof(int), 84 .maxlen = sizeof(int),
85 .mode = 0644, 85 .mode = 0644,
86 .proc_handler = sysctl_laten 86 .proc_handler = sysctl_latencytop,
87 }, 87 },
>> 88 {}
88 }; 89 };
89 #endif 90 #endif
90 91
91 void clear_tsk_latency_tracing(struct task_str 92 void clear_tsk_latency_tracing(struct task_struct *p)
92 { 93 {
93 unsigned long flags; 94 unsigned long flags;
94 95
95 raw_spin_lock_irqsave(&latency_lock, f 96 raw_spin_lock_irqsave(&latency_lock, flags);
96 memset(&p->latency_record, 0, sizeof(p 97 memset(&p->latency_record, 0, sizeof(p->latency_record));
97 p->latency_record_count = 0; 98 p->latency_record_count = 0;
98 raw_spin_unlock_irqrestore(&latency_lo 99 raw_spin_unlock_irqrestore(&latency_lock, flags);
99 } 100 }
100 101
101 static void clear_global_latency_tracing(void) 102 static void clear_global_latency_tracing(void)
102 { 103 {
103 unsigned long flags; 104 unsigned long flags;
104 105
105 raw_spin_lock_irqsave(&latency_lock, f 106 raw_spin_lock_irqsave(&latency_lock, flags);
106 memset(&latency_record, 0, sizeof(late 107 memset(&latency_record, 0, sizeof(latency_record));
107 raw_spin_unlock_irqrestore(&latency_lo 108 raw_spin_unlock_irqrestore(&latency_lock, flags);
108 } 109 }
109 110
110 static void __sched 111 static void __sched
111 account_global_scheduler_latency(struct task_s 112 account_global_scheduler_latency(struct task_struct *tsk,
112 struct latenc 113 struct latency_record *lat)
113 { 114 {
114 int firstnonnull = MAXLR; !! 115 int firstnonnull = MAXLR + 1;
115 int i; 116 int i;
116 117
117 /* skip kernel threads for now */ 118 /* skip kernel threads for now */
118 if (!tsk->mm) 119 if (!tsk->mm)
119 return; 120 return;
120 121
121 for (i = 0; i < MAXLR; i++) { 122 for (i = 0; i < MAXLR; i++) {
122 int q, same = 1; 123 int q, same = 1;
123 124
124 /* Nothing stored: */ 125 /* Nothing stored: */
125 if (!latency_record[i].backtra 126 if (!latency_record[i].backtrace[0]) {
126 if (firstnonnull > i) 127 if (firstnonnull > i)
127 firstnonnull = 128 firstnonnull = i;
128 continue; 129 continue;
129 } 130 }
130 for (q = 0; q < LT_BACKTRACEDE 131 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
131 unsigned long record = 132 unsigned long record = lat->backtrace[q];
132 133
133 if (latency_record[i]. 134 if (latency_record[i].backtrace[q] != record) {
134 same = 0; 135 same = 0;
135 break; 136 break;
136 } 137 }
137 138
138 /* 0 entry marks end o 139 /* 0 entry marks end of backtrace: */
139 if (!record) 140 if (!record)
140 break; 141 break;
141 } 142 }
142 if (same) { 143 if (same) {
143 latency_record[i].coun 144 latency_record[i].count++;
144 latency_record[i].time 145 latency_record[i].time += lat->time;
145 if (lat->time > latenc 146 if (lat->time > latency_record[i].max)
146 latency_record 147 latency_record[i].max = lat->time;
147 return; 148 return;
148 } 149 }
149 } 150 }
150 151
151 i = firstnonnull; 152 i = firstnonnull;
152 if (i >= MAXLR) !! 153 if (i >= MAXLR - 1)
153 return; 154 return;
154 155
155 /* Allocted a new one: */ 156 /* Allocted a new one: */
156 memcpy(&latency_record[i], lat, sizeof 157 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
157 } 158 }
158 159
159 /** 160 /**
160 * __account_scheduler_latency - record an occ 161 * __account_scheduler_latency - record an occurred latency
161 * @tsk - the task struct of the task hitting 162 * @tsk - the task struct of the task hitting the latency
162 * @usecs - the duration of the latency in mic 163 * @usecs - the duration of the latency in microseconds
163 * @inter - 1 if the sleep was interruptible, 164 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
164 * 165 *
165 * This function is the main entry point for r 166 * This function is the main entry point for recording latency entries
166 * as called by the scheduler. 167 * as called by the scheduler.
167 * 168 *
168 * This function has a few special cases to de 169 * This function has a few special cases to deal with normal 'non-latency'
169 * sleeps: specifically, interruptible sleep l 170 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
170 * since this usually is caused by waiting for 171 * since this usually is caused by waiting for events via select() and co.
171 * 172 *
172 * Negative latencies (caused by time going ba 173 * Negative latencies (caused by time going backwards) are also explicitly
173 * skipped. 174 * skipped.
174 */ 175 */
175 void __sched 176 void __sched
176 __account_scheduler_latency(struct task_struct 177 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
177 { 178 {
178 unsigned long flags; 179 unsigned long flags;
179 int i, q; 180 int i, q;
180 struct latency_record lat; 181 struct latency_record lat;
181 182
182 /* Long interruptible waits are genera 183 /* Long interruptible waits are generally user requested... */
183 if (inter && usecs > 5000) 184 if (inter && usecs > 5000)
184 return; 185 return;
185 186
186 /* Negative sleeps are time going back 187 /* Negative sleeps are time going backwards */
187 /* Zero-time sleeps are non-interestin 188 /* Zero-time sleeps are non-interesting */
188 if (usecs <= 0) 189 if (usecs <= 0)
189 return; 190 return;
190 191
191 memset(&lat, 0, sizeof(lat)); 192 memset(&lat, 0, sizeof(lat));
192 lat.count = 1; 193 lat.count = 1;
193 lat.time = usecs; 194 lat.time = usecs;
194 lat.max = usecs; 195 lat.max = usecs;
195 196
196 stack_trace_save_tsk(tsk, lat.backtrac 197 stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0);
197 198
198 raw_spin_lock_irqsave(&latency_lock, f 199 raw_spin_lock_irqsave(&latency_lock, flags);
199 200
200 account_global_scheduler_latency(tsk, 201 account_global_scheduler_latency(tsk, &lat);
201 202
202 for (i = 0; i < tsk->latency_record_co 203 for (i = 0; i < tsk->latency_record_count; i++) {
203 struct latency_record *mylat; 204 struct latency_record *mylat;
204 int same = 1; 205 int same = 1;
205 206
206 mylat = &tsk->latency_record[i 207 mylat = &tsk->latency_record[i];
207 for (q = 0; q < LT_BACKTRACEDE 208 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
208 unsigned long record = 209 unsigned long record = lat.backtrace[q];
209 210
210 if (mylat->backtrace[q 211 if (mylat->backtrace[q] != record) {
211 same = 0; 212 same = 0;
212 break; 213 break;
213 } 214 }
214 215
215 /* 0 entry is end of b 216 /* 0 entry is end of backtrace */
216 if (!record) 217 if (!record)
217 break; 218 break;
218 } 219 }
219 if (same) { 220 if (same) {
220 mylat->count++; 221 mylat->count++;
221 mylat->time += lat.tim 222 mylat->time += lat.time;
222 if (lat.time > mylat-> 223 if (lat.time > mylat->max)
223 mylat->max = l 224 mylat->max = lat.time;
224 goto out_unlock; 225 goto out_unlock;
225 } 226 }
226 } 227 }
227 228
228 /* 229 /*
229 * short term hack; if we're > 32 we s 230 * short term hack; if we're > 32 we stop; future we recycle:
230 */ 231 */
231 if (tsk->latency_record_count >= LT_SA 232 if (tsk->latency_record_count >= LT_SAVECOUNT)
232 goto out_unlock; 233 goto out_unlock;
233 234
234 /* Allocated a new one: */ 235 /* Allocated a new one: */
235 i = tsk->latency_record_count++; 236 i = tsk->latency_record_count++;
236 memcpy(&tsk->latency_record[i], &lat, 237 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
237 238
238 out_unlock: 239 out_unlock:
239 raw_spin_unlock_irqrestore(&latency_lo 240 raw_spin_unlock_irqrestore(&latency_lock, flags);
240 } 241 }
241 242
242 static int lstats_show(struct seq_file *m, voi 243 static int lstats_show(struct seq_file *m, void *v)
243 { 244 {
244 int i; 245 int i;
245 246
246 seq_puts(m, "Latency Top version : v0. 247 seq_puts(m, "Latency Top version : v0.1\n");
247 248
248 for (i = 0; i < MAXLR; i++) { 249 for (i = 0; i < MAXLR; i++) {
249 struct latency_record *lr = &l 250 struct latency_record *lr = &latency_record[i];
250 251
251 if (lr->backtrace[0]) { 252 if (lr->backtrace[0]) {
252 int q; 253 int q;
253 seq_printf(m, "%i %lu 254 seq_printf(m, "%i %lu %lu",
254 lr->count, 255 lr->count, lr->time, lr->max);
255 for (q = 0; q < LT_BAC 256 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
256 unsigned long 257 unsigned long bt = lr->backtrace[q];
257 258
258 if (!bt) 259 if (!bt)
259 break; 260 break;
260 261
261 seq_printf(m, 262 seq_printf(m, " %ps", (void *)bt);
262 } 263 }
263 seq_puts(m, "\n"); 264 seq_puts(m, "\n");
264 } 265 }
265 } 266 }
266 return 0; 267 return 0;
267 } 268 }
268 269
269 static ssize_t 270 static ssize_t
270 lstats_write(struct file *file, const char __u 271 lstats_write(struct file *file, const char __user *buf, size_t count,
271 loff_t *offs) 272 loff_t *offs)
272 { 273 {
273 clear_global_latency_tracing(); 274 clear_global_latency_tracing();
274 275
275 return count; 276 return count;
276 } 277 }
277 278
278 static int lstats_open(struct inode *inode, st 279 static int lstats_open(struct inode *inode, struct file *filp)
279 { 280 {
280 return single_open(filp, lstats_show, 281 return single_open(filp, lstats_show, NULL);
281 } 282 }
282 283
283 static const struct proc_ops lstats_proc_ops = 284 static const struct proc_ops lstats_proc_ops = {
284 .proc_open = lstats_open, 285 .proc_open = lstats_open,
285 .proc_read = seq_read, 286 .proc_read = seq_read,
286 .proc_write = lstats_write, 287 .proc_write = lstats_write,
287 .proc_lseek = seq_lseek, 288 .proc_lseek = seq_lseek,
288 .proc_release = single_release, 289 .proc_release = single_release,
289 }; 290 };
290 291
291 static int __init init_lstats_procfs(void) 292 static int __init init_lstats_procfs(void)
292 { 293 {
293 proc_create("latency_stats", 0644, NUL 294 proc_create("latency_stats", 0644, NULL, &lstats_proc_ops);
294 #ifdef CONFIG_SYSCTL 295 #ifdef CONFIG_SYSCTL
295 register_sysctl_init("kernel", latency 296 register_sysctl_init("kernel", latencytop_sysctl);
296 #endif 297 #endif
297 return 0; 298 return 0;
298 } 299 }
299 device_initcall(init_lstats_procfs); 300 device_initcall(init_lstats_procfs);
300 301
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