~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/latencytop.c

Version: ~ [ linux-5.12 ] ~ [ linux-5.11.16 ] ~ [ linux-5.10.32 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.114 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.188 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.231 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.267 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.267 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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/kallsyms.h>
 51 #include <linux/seq_file.h>
 52 #include <linux/notifier.h>
 53 #include <linux/spinlock.h>
 54 #include <linux/proc_fs.h>
 55 #include <linux/latencytop.h>
 56 #include <linux/export.h>
 57 #include <linux/sched.h>
 58 #include <linux/sched/debug.h>
 59 #include <linux/sched/stat.h>
 60 #include <linux/list.h>
 61 #include <linux/stacktrace.h>
 62 
 63 static DEFINE_RAW_SPINLOCK(latency_lock);
 64 
 65 #define MAXLR 128
 66 static struct latency_record latency_record[MAXLR];
 67 
 68 int latencytop_enabled;
 69 
 70 void clear_all_latency_tracing(struct task_struct *p)
 71 {
 72         unsigned long flags;
 73 
 74         if (!latencytop_enabled)
 75                 return;
 76 
 77         raw_spin_lock_irqsave(&latency_lock, flags);
 78         memset(&p->latency_record, 0, sizeof(p->latency_record));
 79         p->latency_record_count = 0;
 80         raw_spin_unlock_irqrestore(&latency_lock, flags);
 81 }
 82 
 83 static void clear_global_latency_tracing(void)
 84 {
 85         unsigned long flags;
 86 
 87         raw_spin_lock_irqsave(&latency_lock, flags);
 88         memset(&latency_record, 0, sizeof(latency_record));
 89         raw_spin_unlock_irqrestore(&latency_lock, flags);
 90 }
 91 
 92 static void __sched
 93 account_global_scheduler_latency(struct task_struct *tsk,
 94                                  struct latency_record *lat)
 95 {
 96         int firstnonnull = MAXLR + 1;
 97         int i;
 98 
 99         if (!latencytop_enabled)
100                 return;
101 
102         /* skip kernel threads for now */
103         if (!tsk->mm)
104                 return;
105 
106         for (i = 0; i < MAXLR; i++) {
107                 int q, same = 1;
108 
109                 /* Nothing stored: */
110                 if (!latency_record[i].backtrace[0]) {
111                         if (firstnonnull > i)
112                                 firstnonnull = i;
113                         continue;
114                 }
115                 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
116                         unsigned long record = lat->backtrace[q];
117 
118                         if (latency_record[i].backtrace[q] != record) {
119                                 same = 0;
120                                 break;
121                         }
122 
123                         /* 0 and ULONG_MAX entries mean end of backtrace: */
124                         if (record == 0 || record == ULONG_MAX)
125                                 break;
126                 }
127                 if (same) {
128                         latency_record[i].count++;
129                         latency_record[i].time += lat->time;
130                         if (lat->time > latency_record[i].max)
131                                 latency_record[i].max = lat->time;
132                         return;
133                 }
134         }
135 
136         i = firstnonnull;
137         if (i >= MAXLR - 1)
138                 return;
139 
140         /* Allocted a new one: */
141         memcpy(&latency_record[i], lat, sizeof(struct latency_record));
142 }
143 
144 /*
145  * Iterator to store a backtrace into a latency record entry
146  */
147 static inline void store_stacktrace(struct task_struct *tsk,
148                                         struct latency_record *lat)
149 {
150         struct stack_trace trace;
151 
152         memset(&trace, 0, sizeof(trace));
153         trace.max_entries = LT_BACKTRACEDEPTH;
154         trace.entries = &lat->backtrace[0];
155         save_stack_trace_tsk(tsk, &trace);
156 }
157 
158 /**
159  * __account_scheduler_latency - record an occurred latency
160  * @tsk - the task struct of the task hitting the latency
161  * @usecs - the duration of the latency in microseconds
162  * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
163  *
164  * This function is the main entry point for recording latency entries
165  * as called by the scheduler.
166  *
167  * This function has a few special cases to deal with normal 'non-latency'
168  * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
169  * since this usually is caused by waiting for events via select() and co.
170  *
171  * Negative latencies (caused by time going backwards) are also explicitly
172  * skipped.
173  */
174 void __sched
175 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
176 {
177         unsigned long flags;
178         int i, q;
179         struct latency_record lat;
180 
181         /* Long interruptible waits are generally user requested... */
182         if (inter && usecs > 5000)
183                 return;
184 
185         /* Negative sleeps are time going backwards */
186         /* Zero-time sleeps are non-interesting */
187         if (usecs <= 0)
188                 return;
189 
190         memset(&lat, 0, sizeof(lat));
191         lat.count = 1;
192         lat.time = usecs;
193         lat.max = usecs;
194         store_stacktrace(tsk, &lat);
195 
196         raw_spin_lock_irqsave(&latency_lock, flags);
197 
198         account_global_scheduler_latency(tsk, &lat);
199 
200         for (i = 0; i < tsk->latency_record_count; i++) {
201                 struct latency_record *mylat;
202                 int same = 1;
203 
204                 mylat = &tsk->latency_record[i];
205                 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
206                         unsigned long record = lat.backtrace[q];
207 
208                         if (mylat->backtrace[q] != record) {
209                                 same = 0;
210                                 break;
211                         }
212 
213                         /* 0 and ULONG_MAX entries mean end of backtrace: */
214                         if (record == 0 || record == ULONG_MAX)
215                                 break;
216                 }
217                 if (same) {
218                         mylat->count++;
219                         mylat->time += lat.time;
220                         if (lat.time > mylat->max)
221                                 mylat->max = lat.time;
222                         goto out_unlock;
223                 }
224         }
225 
226         /*
227          * short term hack; if we're > 32 we stop; future we recycle:
228          */
229         if (tsk->latency_record_count >= LT_SAVECOUNT)
230                 goto out_unlock;
231 
232         /* Allocated a new one: */
233         i = tsk->latency_record_count++;
234         memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
235 
236 out_unlock:
237         raw_spin_unlock_irqrestore(&latency_lock, flags);
238 }
239 
240 static int lstats_show(struct seq_file *m, void *v)
241 {
242         int i;
243 
244         seq_puts(m, "Latency Top version : v0.1\n");
245 
246         for (i = 0; i < MAXLR; i++) {
247                 struct latency_record *lr = &latency_record[i];
248 
249                 if (lr->backtrace[0]) {
250                         int q;
251                         seq_printf(m, "%i %lu %lu",
252                                    lr->count, lr->time, lr->max);
253                         for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
254                                 unsigned long bt = lr->backtrace[q];
255                                 if (!bt)
256                                         break;
257                                 if (bt == ULONG_MAX)
258                                         break;
259                                 seq_printf(m, " %ps", (void *)bt);
260                         }
261                         seq_puts(m, "\n");
262                 }
263         }
264         return 0;
265 }
266 
267 static ssize_t
268 lstats_write(struct file *file, const char __user *buf, size_t count,
269              loff_t *offs)
270 {
271         clear_global_latency_tracing();
272 
273         return count;
274 }
275 
276 static int lstats_open(struct inode *inode, struct file *filp)
277 {
278         return single_open(filp, lstats_show, NULL);
279 }
280 
281 static const struct file_operations lstats_fops = {
282         .open           = lstats_open,
283         .read           = seq_read,
284         .write          = lstats_write,
285         .llseek         = seq_lseek,
286         .release        = single_release,
287 };
288 
289 static int __init init_lstats_procfs(void)
290 {
291         proc_create("latency_stats", 0644, NULL, &lstats_fops);
292         return 0;
293 }
294 
295 int sysctl_latencytop(struct ctl_table *table, int write,
296                         void __user *buffer, size_t *lenp, loff_t *ppos)
297 {
298         int err;
299 
300         err = proc_dointvec(table, write, buffer, lenp, ppos);
301         if (latencytop_enabled)
302                 force_schedstat_enabled();
303 
304         return err;
305 }
306 device_initcall(init_lstats_procfs);
307 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp