2 * latencytop.c: Latency display infrastructure
4 * (C) Copyright 2008 Intel Corporation
5 * Author: Arjan van de Ven <arjan@linux.intel.com>
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
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.
20 * This code tracks 2 levels of statistics:
21 * 1) System level latency
22 * 2) Per process latency
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.
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.
35 * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
36 * These files look like this:
38 * Latency Top version : v0.1
39 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
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
46 * (note: the average latency is the accumulated latency divided by the number
50 #include <linux/latencytop.h>
51 #include <linux/kallsyms.h>
52 #include <linux/seq_file.h>
53 #include <linux/notifier.h>
54 #include <linux/spinlock.h>
55 #include <linux/proc_fs.h>
56 #include <linux/module.h>
57 #include <linux/sched.h>
58 #include <linux/list.h>
59 #include <linux/slab.h>
60 #include <linux/stacktrace.h>
62 static DEFINE_SPINLOCK(latency_lock);
65 static struct latency_record latency_record[MAXLR];
67 int latencytop_enabled;
69 void clear_all_latency_tracing(struct task_struct *p)
73 if (!latencytop_enabled)
76 spin_lock_irqsave(&latency_lock, flags);
77 memset(&p->latency_record, 0, sizeof(p->latency_record));
78 p->latency_record_count = 0;
79 spin_unlock_irqrestore(&latency_lock, flags);
82 static void clear_global_latency_tracing(void)
86 spin_lock_irqsave(&latency_lock, flags);
87 memset(&latency_record, 0, sizeof(latency_record));
88 spin_unlock_irqrestore(&latency_lock, flags);
92 account_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat)
94 int firstnonnull = MAXLR + 1;
97 if (!latencytop_enabled)
100 /* skip kernel threads for now */
104 for (i = 0; i < MAXLR; i++) {
107 /* Nothing stored: */
108 if (!latency_record[i].backtrace[0]) {
109 if (firstnonnull > i)
113 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
114 unsigned long record = lat->backtrace[q];
116 if (latency_record[i].backtrace[q] != record) {
121 /* 0 and ULONG_MAX entries mean end of backtrace: */
122 if (record == 0 || record == ULONG_MAX)
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;
138 /* Allocted a new one: */
139 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
143 * Iterator to store a backtrace into a latency record entry
145 static inline void store_stacktrace(struct task_struct *tsk,
146 struct latency_record *lat)
148 struct stack_trace trace;
150 memset(&trace, 0, sizeof(trace));
151 trace.max_entries = LT_BACKTRACEDEPTH;
152 trace.entries = &lat->backtrace[0];
153 save_stack_trace_tsk(tsk, &trace);
157 * __account_scheduler_latency - record an occured latency
158 * @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
162 * This function is the main entry point for recording latency entries
163 * as called by the scheduler.
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.
169 * Negative latencies (caused by time going backwards) are also explicitly
173 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
177 struct latency_record lat;
179 /* Long interruptible waits are generally user requested... */
180 if (inter && usecs > 5000)
183 /* Negative sleeps are time going backwards */
184 /* Zero-time sleeps are non-interesting */
188 memset(&lat, 0, sizeof(lat));
192 store_stacktrace(tsk, &lat);
194 spin_lock_irqsave(&latency_lock, flags);
196 account_global_scheduler_latency(tsk, &lat);
198 for (i = 0; i < tsk->latency_record_count; i++) {
199 struct latency_record *mylat;
202 mylat = &tsk->latency_record[i];
203 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
204 unsigned long record = lat.backtrace[q];
206 if (mylat->backtrace[q] != record) {
211 /* 0 and ULONG_MAX entries mean end of backtrace: */
212 if (record == 0 || record == ULONG_MAX)
217 mylat->time += lat.time;
218 if (lat.time > mylat->max)
219 mylat->max = lat.time;
225 * short term hack; if we're > 32 we stop; future we recycle:
227 if (tsk->latency_record_count >= LT_SAVECOUNT)
230 /* Allocated a new one: */
231 i = tsk->latency_record_count++;
232 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
235 spin_unlock_irqrestore(&latency_lock, flags);
238 static int lstats_show(struct seq_file *m, void *v)
242 seq_puts(m, "Latency Top version : v0.1\n");
244 for (i = 0; i < MAXLR; i++) {
245 if (latency_record[i].backtrace[0]) {
247 seq_printf(m, "%i %lu %lu ",
248 latency_record[i].count,
249 latency_record[i].time,
250 latency_record[i].max);
251 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
252 char sym[KSYM_SYMBOL_LEN];
254 if (!latency_record[i].backtrace[q])
256 if (latency_record[i].backtrace[q] == ULONG_MAX)
258 sprint_symbol(sym, latency_record[i].backtrace[q]);
259 c = strchr(sym, '+');
262 seq_printf(m, "%s ", sym);
271 lstats_write(struct file *file, const char __user *buf, size_t count,
274 clear_global_latency_tracing();
279 static int lstats_open(struct inode *inode, struct file *filp)
281 return single_open(filp, lstats_show, NULL);
284 static const struct file_operations lstats_fops = {
287 .write = lstats_write,
289 .release = single_release,
292 static int __init init_lstats_procfs(void)
294 proc_create("latency_stats", 0644, NULL, &lstats_fops);
297 device_initcall(init_lstats_procfs);