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73784b3 @umeshkrishnan Base line for SHIVA - Based from PSP 3.00.01.06
umeshkrishnan authored
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/slab.h>
60 #include <linux/stacktrace.h>
61
62 static DEFINE_SPINLOCK(latency_lock);
63
64 #define MAXLR 128
65 static struct latency_record latency_record[MAXLR];
66
67 int latencytop_enabled;
68
69 void clear_all_latency_tracing(struct task_struct *p)
70 {
71 unsigned long flags;
72
73 if (!latencytop_enabled)
74 return;
75
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);
80 }
81
82 static void clear_global_latency_tracing(void)
83 {
84 unsigned long flags;
85
86 spin_lock_irqsave(&latency_lock, flags);
87 memset(&latency_record, 0, sizeof(latency_record));
88 spin_unlock_irqrestore(&latency_lock, flags);
89 }
90
91 static void __sched
92 account_global_scheduler_latency(struct task_struct *tsk, struct latency_record *lat)
93 {
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++) {
105 int q, same = 1;
106
107 /* Nothing stored: */
108 if (!latency_record[i].backtrace[0]) {
109 if (firstnonnull > i)
110 firstnonnull = i;
111 continue;
112 }
113 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
114 unsigned long record = lat->backtrace[q];
115
116 if (latency_record[i].backtrace[q] != record) {
117 same = 0;
118 break;
119 }
120
121 /* 0 and ULONG_MAX entries mean end of backtrace: */
122 if (record == 0 || record == ULONG_MAX)
123 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
142 /*
143 * Iterator to store a backtrace into a latency record entry
144 */
145 static inline void store_stacktrace(struct task_struct *tsk,
146 struct latency_record *lat)
147 {
148 struct stack_trace trace;
149
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);
154 }
155
156 /**
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
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 */
172 void __sched
173 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
174 {
175 unsigned long flags;
176 int i, q;
177 struct latency_record lat;
178
179 /* Long interruptible waits are generally user requested... */
180 if (inter && usecs > 5000)
181 return;
182
183 /* Negative sleeps are time going backwards */
184 /* Zero-time sleeps are non-interesting */
185 if (usecs <= 0)
186 return;
187
188 memset(&lat, 0, sizeof(lat));
189 lat.count = 1;
190 lat.time = usecs;
191 lat.max = usecs;
192 store_stacktrace(tsk, &lat);
193
194 spin_lock_irqsave(&latency_lock, flags);
195
196 account_global_scheduler_latency(tsk, &lat);
197
198 /*
199 * short term hack; if we're > 32 we stop; future we recycle:
200 */
201 tsk->latency_record_count++;
202 if (tsk->latency_record_count >= LT_SAVECOUNT)
203 goto out_unlock;
204
205 for (i = 0; i < LT_SAVECOUNT; i++) {
206 struct latency_record *mylat;
207 int same = 1;
208
209 mylat = &tsk->latency_record[i];
210 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
211 unsigned long record = lat.backtrace[q];
212
213 if (mylat->backtrace[q] != record) {
214 same = 0;
215 break;
216 }
217
218 /* 0 and ULONG_MAX entries mean end of backtrace: */
219 if (record == 0 || record == ULONG_MAX)
220 break;
221 }
222 if (same) {
223 mylat->count++;
224 mylat->time += lat.time;
225 if (lat.time > mylat->max)
226 mylat->max = lat.time;
227 goto out_unlock;
228 }
229 }
230
231 /* Allocated a new one: */
232 i = tsk->latency_record_count;
233 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
234
235 out_unlock:
236 spin_unlock_irqrestore(&latency_lock, flags);
237 }
238
239 static int lstats_show(struct seq_file *m, void *v)
240 {
241 int i;
242
243 seq_puts(m, "Latency Top version : v0.1\n");
244
245 for (i = 0; i < MAXLR; i++) {
246 if (latency_record[i].backtrace[0]) {
247 int q;
248 seq_printf(m, "%i %lu %lu ",
249 latency_record[i].count,
250 latency_record[i].time,
251 latency_record[i].max);
252 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
253 char sym[KSYM_SYMBOL_LEN];
254 char *c;
255 if (!latency_record[i].backtrace[q])
256 break;
257 if (latency_record[i].backtrace[q] == ULONG_MAX)
258 break;
259 sprint_symbol(sym, latency_record[i].backtrace[q]);
260 c = strchr(sym, '+');
261 if (c)
262 *c = 0;
263 seq_printf(m, "%s ", sym);
264 }
265 seq_printf(m, "\n");
266 }
267 }
268 return 0;
269 }
270
271 static ssize_t
272 lstats_write(struct file *file, const char __user *buf, size_t count,
273 loff_t *offs)
274 {
275 clear_global_latency_tracing();
276
277 return count;
278 }
279
280 static int lstats_open(struct inode *inode, struct file *filp)
281 {
282 return single_open(filp, lstats_show, NULL);
283 }
284
285 static const struct file_operations lstats_fops = {
286 .open = lstats_open,
287 .read = seq_read,
288 .write = lstats_write,
289 .llseek = seq_lseek,
290 .release = single_release,
291 };
292
293 static int __init init_lstats_procfs(void)
294 {
295 proc_create("latency_stats", 0644, NULL, &lstats_fops);
296 return 0;
297 }
298 device_initcall(init_lstats_procfs);
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