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1 | /* | |
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 | */ | |
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 | ||
61 | static DEFINE_SPINLOCK(latency_lock); | |
62 | ||
63 | #define MAXLR 128 | |
64 | static struct latency_record latency_record[MAXLR]; | |
65 | ||
66 | int latencytop_enabled; | |
67 | ||
68 | void 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 | ||
81 | static 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 | ||
90 | static void __sched | |
91 | account_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 | */ | |
144 | static 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 | */ | |
171 | void __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 | ||
233 | out_unlock: | |
234 | spin_unlock_irqrestore(&latency_lock, flags); | |
235 | } | |
236 | ||
237 | static 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 | ||
264 | static ssize_t | |
265 | lstats_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 | ||
273 | static int lstats_open(struct inode *inode, struct file *filp) | |
274 | { | |
275 | return single_open(filp, lstats_show, NULL); | |
276 | } | |
277 | ||
278 | static 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 | ||
286 | static int __init init_lstats_procfs(void) | |
287 | { | |
288 | proc_create("latency_stats", 0644, NULL, &lstats_fops); | |
289 | return 0; | |
290 | } | |
291 | device_initcall(init_lstats_procfs); |