projects/linux·blob v3.1 · refs

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1/*
2 * latencytop.c: Latency display infrastructure
3 *
4 * (C) Copyright 2008 Intel Corporation
5 * Author: Arjan van de Ven <[email protected]>
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 */
12
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
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/stacktrace.h>
60
61static DEFINE_SPINLOCK(latency_lock);
62
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
75 spin_lock_irqsave(&latency_lock, flags);
76 memset(&p->latency_record, 0, sizeof(p->latency_record));
77 p->latency_record_count = 0;
78 spin_unlock_irqrestore(&latency_lock, flags);
79}
80
81static void clear_global_latency_tracing(void)
82{
83 unsigned long flags;
84
85 spin_lock_irqsave(&latency_lock, flags);
86 memset(&latency_record, 0, sizeof(latency_record));
87 spin_unlock_irqrestore(&latency_lock, flags);
88}
89
90static void __sched
91account_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat)
92{
93 int firstnonnull = MAXLR + 1;
94 int i;
95
96 if (!latencytop_enabled)
97 return;
98
99 /* skip kernel threads for now */
100 if (!tsk->mm)
101 return;
102
103 for (i = 0; i < MAXLR; i++) {
104 int q, same = 1;
105
106 /* Nothing stored: */
107 if (!latency_record[i].backtrace[0]) {
108 if (firstnonnull > i)
109 firstnonnull = i;
110 continue;
111 }
112 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
113 unsigned long record = lat->backtrace[q];
114
115 if (latency_record[i].backtrace[q] != record) {
116 same = 0;
117 break;
118 }
119
120 /* 0 and ULONG_MAX entries mean end of backtrace: */
121 if (record == 0 || record == ULONG_MAX)
122 break;
123 }
124 if (same) {
125 latency_record[i].count++;
126 latency_record[i].time += lat->time;
127 if (lat->time > latency_record[i].max)
128 latency_record[i].max = lat->time;
129 return;
130 }
131 }
132
133 i = firstnonnull;
134 if (i >= MAXLR - 1)
135 return;
136
137 /* Allocted a new one: */
138 memcpy(&latency_record[i], lat, sizeof(struct latency_record));
139}
140
141/*
142 * Iterator to store a backtrace into a latency record entry
143 */
144static inline void store_stacktrace(struct task_struct *tsk,
145 struct latency_record *lat)
146{
147 struct stack_trace trace;
148
149 memset(&trace, 0, sizeof(trace));
150 trace.max_entries = LT_BACKTRACEDEPTH;
151 trace.entries = &lat->backtrace[0];
152 save_stack_trace_tsk(tsk, &trace);
153}
154
155/**
156 * __account_scheduler_latency - record an occurred latency
157 * @tsk - the task struct of the task hitting the latency
158 * @usecs - the duration of the latency in microseconds
159 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
160 *
161 * This function is the main entry point for recording latency entries
162 * as called by the scheduler.
163 *
164 * This function has a few special cases to deal with normal 'non-latency'
165 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
166 * since this usually is caused by waiting for events via select() and co.
167 *
168 * Negative latencies (caused by time going backwards) are also explicitly
169 * skipped.
170 */
171void __sched
172__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
173{
174 unsigned long flags;
175 int i, q;
176 struct latency_record lat;
177
178 /* Long interruptible waits are generally user requested... */
179 if (inter && usecs > 5000)
180 return;
181
182 /* Negative sleeps are time going backwards */
183 /* Zero-time sleeps are non-interesting */
184 if (usecs <= 0)
185 return;
186
187 memset(&lat, 0, sizeof(lat));
188 lat.count = 1;
189 lat.time = usecs;
190 lat.max = usecs;
191 store_stacktrace(tsk, &lat);
192
193 spin_lock_irqsave(&latency_lock, flags);
194
195 account_global_scheduler_latency(tsk, &lat);
196
197 for (i = 0; i < tsk->latency_record_count; i++) {
198 struct latency_record *mylat;
199 int same = 1;
200
201 mylat = &tsk->latency_record[i];
202 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
203 unsigned long record = lat.backtrace[q];
204
205 if (mylat->backtrace[q] != record) {
206 same = 0;
207 break;
208 }
209
210 /* 0 and ULONG_MAX entries mean end of backtrace: */
211 if (record == 0 || record == ULONG_MAX)
212 break;
213 }
214 if (same) {
215 mylat->count++;
216 mylat->time += lat.time;
217 if (lat.time > mylat->max)
218 mylat->max = lat.time;
219 goto out_unlock;
220 }
221 }
222
223 /*
224 * short term hack; if we're > 32 we stop; future we recycle:
225 */
226 if (tsk->latency_record_count >= LT_SAVECOUNT)
227 goto out_unlock;
228
229 /* Allocated a new one: */
230 i = tsk->latency_record_count++;
231 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
232
233out_unlock:
234 spin_unlock_irqrestore(&latency_lock, flags);
235}
236
237static int lstats_show(struct seq_file *m, void *v)
238{
239 int i;
240
241 seq_puts(m, "Latency Top version : v0.1\n");
242
243 for (i = 0; i < MAXLR; i++) {
244 struct latency_record *lr = &latency_record[i];
245
246 if (lr->backtrace[0]) {
247 int q;
248 seq_printf(m, "%i %lu %lu",
249 lr->count, lr->time, lr->max);
250 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
251 unsigned long bt = lr->backtrace[q];
252 if (!bt)
253 break;
254 if (bt == ULONG_MAX)
255 break;
256 seq_printf(m, " %ps", (void *)bt);
257 }
258 seq_printf(m, "\n");
259 }
260 }
261 return 0;
262}
263
264static ssize_t
265lstats_write(struct file *file, const char __user *buf, size_t count,
266 loff_t *offs)
267{
268 clear_global_latency_tracing();
269
270 return count;
271}
272
273static int lstats_open(struct inode *inode, struct file *filp)
274{
275 return single_open(filp, lstats_show, NULL);
276}
277
278static const struct file_operations lstats_fops = {
279 .open = lstats_open,
280 .read = seq_read,
281 .write = lstats_write,
282 .llseek = seq_lseek,
283 .release = single_release,
284};
285
286static int __init init_lstats_procfs(void)
287{
288 proc_create("latency_stats", 0644, NULL, &lstats_fops);
289 return 0;
290}
291device_initcall(init_lstats_procfs);