kernel/latencytop.c

   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);