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Arjan van de Ven97455122008-01-25 21:08:34 +01001/*
2 * latencytop.c: Latency display infrastructure
3 *
4 * (C) Copyright 2008 Intel Corporation
5 * Author: Arjan van de Ven <arjan@linux.intel.com>
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; version 2
10 * of the License.
11 */
Arjan van de Venad0b0fd552009-02-10 11:42:26 -080012
13/*
14 * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
15 * used by the "latencytop" userspace tool. The latency that is tracked is not
16 * the 'traditional' interrupt latency (which is primarily caused by something
17 * else consuming CPU), but instead, it is the latency an application encounters
18 * because the kernel sleeps on its behalf for various reasons.
19 *
20 * This code tracks 2 levels of statistics:
21 * 1) System level latency
22 * 2) Per process latency
23 *
24 * The latency is stored in fixed sized data structures in an accumulated form;
25 * if the "same" latency cause is hit twice, this will be tracked as one entry
26 * in the data structure. Both the count, total accumulated latency and maximum
27 * latency are tracked in this data structure. When the fixed size structure is
28 * full, no new causes are tracked until the buffer is flushed by writing to
29 * the /proc file; the userspace tool does this on a regular basis.
30 *
31 * A latency cause is identified by a stringified backtrace at the point that
32 * the scheduler gets invoked. The userland tool will use this string to
33 * identify the cause of the latency in human readable form.
34 *
35 * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
36 * These files look like this:
37 *
38 * Latency Top version : v0.1
39 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
40 * | | | |
41 * | | | +----> the stringified backtrace
42 * | | +---------> The maximum latency for this entry in microseconds
43 * | +--------------> The accumulated latency for this entry (microseconds)
44 * +-------------------> The number of times this entry is hit
45 *
46 * (note: the average latency is the accumulated latency divided by the number
47 * of times)
48 */
49
Arjan van de Ven97455122008-01-25 21:08:34 +010050#include <linux/kallsyms.h>
51#include <linux/seq_file.h>
52#include <linux/notifier.h>
53#include <linux/spinlock.h>
54#include <linux/proc_fs.h>
Mel Gormancb251762016-02-05 09:08:36 +000055#include <linux/latencytop.h>
Paul Gortmaker9984de12011-05-23 14:51:41 -040056#include <linux/export.h>
Arjan van de Ven97455122008-01-25 21:08:34 +010057#include <linux/sched.h>
58#include <linux/list.h>
Arjan van de Ven97455122008-01-25 21:08:34 +010059#include <linux/stacktrace.h>
60
Thomas Gleixner757455d2009-09-17 17:31:09 +020061static DEFINE_RAW_SPINLOCK(latency_lock);
Arjan van de Ven97455122008-01-25 21:08:34 +010062
63#define MAXLR 128
64static struct latency_record latency_record[MAXLR];
65
66int latencytop_enabled;
67
68void clear_all_latency_tracing(struct task_struct *p)
69{
70 unsigned long flags;
71
72 if (!latencytop_enabled)
73 return;
74
Thomas Gleixner757455d2009-09-17 17:31:09 +020075 raw_spin_lock_irqsave(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +010076 memset(&p->latency_record, 0, sizeof(p->latency_record));
77 p->latency_record_count = 0;
Thomas Gleixner757455d2009-09-17 17:31:09 +020078 raw_spin_unlock_irqrestore(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +010079}
80
81static void clear_global_latency_tracing(void)
82{
83 unsigned long flags;
84
Thomas Gleixner757455d2009-09-17 17:31:09 +020085 raw_spin_lock_irqsave(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +010086 memset(&latency_record, 0, sizeof(latency_record));
Thomas Gleixner757455d2009-09-17 17:31:09 +020087 raw_spin_unlock_irqrestore(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +010088}
89
90static void __sched
Fabian Frederickeaa18092014-06-04 16:11:21 -070091account_global_scheduler_latency(struct task_struct *tsk,
92 struct latency_record *lat)
Arjan van de Ven97455122008-01-25 21:08:34 +010093{
94 int firstnonnull = MAXLR + 1;
95 int i;
96
97 if (!latencytop_enabled)
98 return;
99
100 /* skip kernel threads for now */
101 if (!tsk->mm)
102 return;
103
104 for (i = 0; i < MAXLR; i++) {
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100105 int q, same = 1;
106
Arjan van de Ven97455122008-01-25 21:08:34 +0100107 /* Nothing stored: */
108 if (!latency_record[i].backtrace[0]) {
109 if (firstnonnull > i)
110 firstnonnull = i;
111 continue;
112 }
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800113 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100114 unsigned long record = lat->backtrace[q];
115
116 if (latency_record[i].backtrace[q] != record) {
Arjan van de Ven97455122008-01-25 21:08:34 +0100117 same = 0;
Arjan van de Ven97455122008-01-25 21:08:34 +0100118 break;
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100119 }
120
121 /* 0 and ULONG_MAX entries mean end of backtrace: */
122 if (record == 0 || record == ULONG_MAX)
Arjan van de Ven97455122008-01-25 21:08:34 +0100123 break;
124 }
125 if (same) {
126 latency_record[i].count++;
127 latency_record[i].time += lat->time;
128 if (lat->time > latency_record[i].max)
129 latency_record[i].max = lat->time;
130 return;
131 }
132 }
133
134 i = firstnonnull;
135 if (i >= MAXLR - 1)
136 return;
137
138 /* Allocted a new one: */
139 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
140}
141
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800142/*
143 * Iterator to store a backtrace into a latency record entry
144 */
145static inline void store_stacktrace(struct task_struct *tsk,
146 struct latency_record *lat)
Arjan van de Ven97455122008-01-25 21:08:34 +0100147{
148 struct stack_trace trace;
149
150 memset(&trace, 0, sizeof(trace));
151 trace.max_entries = LT_BACKTRACEDEPTH;
152 trace.entries = &lat->backtrace[0];
Arjan van de Ven97455122008-01-25 21:08:34 +0100153 save_stack_trace_tsk(tsk, &trace);
154}
155
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800156/**
Lucas De Marchi25985ed2011-03-30 22:57:33 -0300157 * __account_scheduler_latency - record an occurred latency
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800158 * @tsk - the task struct of the task hitting the latency
159 * @usecs - the duration of the latency in microseconds
160 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
161 *
162 * This function is the main entry point for recording latency entries
163 * as called by the scheduler.
164 *
165 * This function has a few special cases to deal with normal 'non-latency'
166 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
167 * since this usually is caused by waiting for events via select() and co.
168 *
169 * Negative latencies (caused by time going backwards) are also explicitly
170 * skipped.
171 */
Arjan van de Ven97455122008-01-25 21:08:34 +0100172void __sched
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800173__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
Arjan van de Ven97455122008-01-25 21:08:34 +0100174{
175 unsigned long flags;
176 int i, q;
177 struct latency_record lat;
178
Arjan van de Ven97455122008-01-25 21:08:34 +0100179 /* Long interruptible waits are generally user requested... */
180 if (inter && usecs > 5000)
181 return;
182
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800183 /* Negative sleeps are time going backwards */
184 /* Zero-time sleeps are non-interesting */
185 if (usecs <= 0)
186 return;
187
Arjan van de Ven97455122008-01-25 21:08:34 +0100188 memset(&lat, 0, sizeof(lat));
189 lat.count = 1;
190 lat.time = usecs;
191 lat.max = usecs;
192 store_stacktrace(tsk, &lat);
193
Thomas Gleixner757455d2009-09-17 17:31:09 +0200194 raw_spin_lock_irqsave(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +0100195
196 account_global_scheduler_latency(tsk, &lat);
197
Ken Chen38715252010-11-11 14:05:16 -0800198 for (i = 0; i < tsk->latency_record_count; i++) {
Arjan van de Ven97455122008-01-25 21:08:34 +0100199 struct latency_record *mylat;
200 int same = 1;
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100201
Arjan van de Ven97455122008-01-25 21:08:34 +0100202 mylat = &tsk->latency_record[i];
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800203 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100204 unsigned long record = lat.backtrace[q];
205
206 if (mylat->backtrace[q] != record) {
Arjan van de Ven97455122008-01-25 21:08:34 +0100207 same = 0;
Arjan van de Ven97455122008-01-25 21:08:34 +0100208 break;
Dmitry Adamushko19fb5182008-02-17 22:34:07 +0100209 }
210
211 /* 0 and ULONG_MAX entries mean end of backtrace: */
212 if (record == 0 || record == ULONG_MAX)
Arjan van de Ven97455122008-01-25 21:08:34 +0100213 break;
214 }
215 if (same) {
216 mylat->count++;
217 mylat->time += lat.time;
218 if (lat.time > mylat->max)
219 mylat->max = lat.time;
220 goto out_unlock;
221 }
222 }
223
Ken Chen38715252010-11-11 14:05:16 -0800224 /*
225 * short term hack; if we're > 32 we stop; future we recycle:
226 */
227 if (tsk->latency_record_count >= LT_SAVECOUNT)
228 goto out_unlock;
229
Arjan van de Ven97455122008-01-25 21:08:34 +0100230 /* Allocated a new one: */
Ken Chen38715252010-11-11 14:05:16 -0800231 i = tsk->latency_record_count++;
Arjan van de Ven97455122008-01-25 21:08:34 +0100232 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
233
234out_unlock:
Thomas Gleixner757455d2009-09-17 17:31:09 +0200235 raw_spin_unlock_irqrestore(&latency_lock, flags);
Arjan van de Ven97455122008-01-25 21:08:34 +0100236}
237
238static int lstats_show(struct seq_file *m, void *v)
239{
240 int i;
241
242 seq_puts(m, "Latency Top version : v0.1\n");
243
244 for (i = 0; i < MAXLR; i++) {
Joe Perches34e49d42011-01-12 17:00:30 -0800245 struct latency_record *lr = &latency_record[i];
246
247 if (lr->backtrace[0]) {
Arjan van de Ven97455122008-01-25 21:08:34 +0100248 int q;
Joe Perches34e49d42011-01-12 17:00:30 -0800249 seq_printf(m, "%i %lu %lu",
250 lr->count, lr->time, lr->max);
Arjan van de Ven97455122008-01-25 21:08:34 +0100251 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
Joe Perches34e49d42011-01-12 17:00:30 -0800252 unsigned long bt = lr->backtrace[q];
253 if (!bt)
Arjan van de Ven97455122008-01-25 21:08:34 +0100254 break;
Joe Perches34e49d42011-01-12 17:00:30 -0800255 if (bt == ULONG_MAX)
Arjan van de Ven97455122008-01-25 21:08:34 +0100256 break;
Joe Perches34e49d42011-01-12 17:00:30 -0800257 seq_printf(m, " %ps", (void *)bt);
Arjan van de Ven97455122008-01-25 21:08:34 +0100258 }
Fabian Frederickeaa18092014-06-04 16:11:21 -0700259 seq_puts(m, "\n");
Arjan van de Ven97455122008-01-25 21:08:34 +0100260 }
261 }
262 return 0;
263}
264
265static ssize_t
266lstats_write(struct file *file, const char __user *buf, size_t count,
267 loff_t *offs)
268{
269 clear_global_latency_tracing();
270
271 return count;
272}
273
274static int lstats_open(struct inode *inode, struct file *filp)
275{
276 return single_open(filp, lstats_show, NULL);
277}
278
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800279static const struct file_operations lstats_fops = {
Arjan van de Ven97455122008-01-25 21:08:34 +0100280 .open = lstats_open,
281 .read = seq_read,
282 .write = lstats_write,
283 .llseek = seq_lseek,
284 .release = single_release,
285};
286
287static int __init init_lstats_procfs(void)
288{
Denis V. Lunevc33fff02008-04-29 01:02:31 -0700289 proc_create("latency_stats", 0644, NULL, &lstats_fops);
Arjan van de Ven97455122008-01-25 21:08:34 +0100290 return 0;
291}
Mel Gormancb251762016-02-05 09:08:36 +0000292
293int sysctl_latencytop(struct ctl_table *table, int write,
294 void __user *buffer, size_t *lenp, loff_t *ppos)
295{
296 int err;
297
298 err = proc_dointvec(table, write, buffer, lenp, ppos);
299 if (latencytop_enabled)
300 force_schedstat_enabled();
301
302 return err;
303}
Arjan van de Venad0b0fd552009-02-10 11:42:26 -0800304device_initcall(init_lstats_procfs);