kernel/latencytop.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * latencytop.c: Latency display infrastructure
   4  *
   5  * (C) Copyright 2008 Intel Corporation
   6  * Author: Arjan van de Ven <arjan@linux.intel.com>
   7  */
   8
   9 /*
  10  * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
  11  * used by the "latencytop" userspace tool. The latency that is tracked is not
  12  * the 'traditional' interrupt latency (which is primarily caused by something
  13  * else consuming CPU), but instead, it is the latency an application encounters
  14  * because the kernel sleeps on its behalf for various reasons.
  15  *
  16  * This code tracks 2 levels of statistics:
  17  * 1) System level latency
  18  * 2) Per process latency
  19  *
  20  * The latency is stored in fixed sized data structures in an accumulated form;
  21  * if the "same" latency cause is hit twice, this will be tracked as one entry
  22  * in the data structure. Both the count, total accumulated latency and maximum
  23  * latency are tracked in this data structure. When the fixed size structure is
  24  * full, no new causes are tracked until the buffer is flushed by writing to
  25  * the /proc file; the userspace tool does this on a regular basis.
  26  *
  27  * A latency cause is identified by a stringified backtrace at the point that
  28  * the scheduler gets invoked. The userland tool will use this string to
  29  * identify the cause of the latency in human readable form.
  30  *
  31  * The information is exported via /proc/latency_stats and /proc/<pid>/latency.
  32  * These files look like this:
  33  *
  34  * Latency Top version : v0.1
  35  * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
  36  * |    |    |    |
  37  * |    |    |    +----> the stringified backtrace
  38  * |    |    +---------> The maximum latency for this entry in microseconds
  39  * |    +--------------> The accumulated latency for this entry (microseconds)
  40  * +-------------------> The number of times this entry is hit
  41  *
  42  * (note: the average latency is the accumulated latency divided by the number
  43  * of times)
  44  */
  45
  46 #include <linux/kallsyms.h>
  47 #include <linux/seq_file.h>
  48 #include <linux/notifier.h>
  49 #include <linux/spinlock.h>
  50 #include <linux/proc_fs.h>
  51 #include <linux/latencytop.h>
  52 #include <linux/export.h>
  53 #include <linux/sched.h>
  54 #include <linux/sched/debug.h>
  55 #include <linux/sched/stat.h>
  56 #include <linux/list.h>
  57 #include <linux/stacktrace.h>
  58
  59 static DEFINE_RAW_SPINLOCK(latency_lock);
  60
  61 #define MAXLR 128
  62 static struct latency_record latency_record[MAXLR];
  63
  64 int latencytop_enabled;
  65
  66 void clear_tsk_latency_tracing(struct task_struct *p)
  67 {
  68         unsigned long flags;
  69
  70         raw_spin_lock_irqsave(&latency_lock, flags);
  71         memset(&p->latency_record, 0, sizeof(p->latency_record));
  72         p->latency_record_count = 0;
  73         raw_spin_unlock_irqrestore(&latency_lock, flags);
  74 }
  75
  76 static void clear_global_latency_tracing(void)
  77 {
  78         unsigned long flags;
  79
  80         raw_spin_lock_irqsave(&latency_lock, flags);
  81         memset(&latency_record, 0, sizeof(latency_record));
  82         raw_spin_unlock_irqrestore(&latency_lock, flags);
  83 }
  84
  85 static void __sched
  86 account_global_scheduler_latency(struct task_struct *tsk,
  87                                  struct latency_record *lat)
  88 {
  89         int firstnonnull = MAXLR + 1;
  90         int i;
  91
  92         /* skip kernel threads for now */
  93         if (!tsk->mm)
  94                 return;
  95
  96         for (i = 0; i < MAXLR; i++) {
  97                 int q, same = 1;
  98
  99                 /* Nothing stored: */
 100                 if (!latency_record[i].backtrace[0]) {
 101                         if (firstnonnull > i)
 102                                 firstnonnull = i;
 103                         continue;
 104                 }
 105                 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
 106                         unsigned long record = lat->backtrace[q];
 107
 108                         if (latency_record[i].backtrace[q] != record) {
 109                                 same = 0;
 110                                 break;
 111                         }
 112
 113                         /* 0 entry marks end of backtrace: */
 114                         if (!record)
 115                                 break;
 116                 }
 117                 if (same) {
 118                         latency_record[i].count++;
 119                         latency_record[i].time += lat->time;
 120                         if (lat->time > latency_record[i].max)
 121                                 latency_record[i].max = lat->time;
 122                         return;
 123                 }
 124         }
 125
 126         i = firstnonnull;
 127         if (i >= MAXLR - 1)
 128                 return;
 129
 130         /* Allocted a new one: */
 131         memcpy(&latency_record[i], lat, sizeof(struct latency_record));
 132 }
 133
 134 /**
 135  * __account_scheduler_latency - record an occurred latency
 136  * @tsk - the task struct of the task hitting the latency
 137  * @usecs - the duration of the latency in microseconds
 138  * @inter - 1 if the sleep was interruptible, 0 if uninterruptible
 139  *
 140  * This function is the main entry point for recording latency entries
 141  * as called by the scheduler.
 142  *
 143  * This function has a few special cases to deal with normal 'non-latency'
 144  * sleeps: specifically, interruptible sleep longer than 5 msec is skipped
 145  * since this usually is caused by waiting for events via select() and co.
 146  *
 147  * Negative latencies (caused by time going backwards) are also explicitly
 148  * skipped.
 149  */
 150 void __sched
 151 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
 152 {
 153         unsigned long flags;
 154         int i, q;
 155         struct latency_record lat;
 156
 157         /* Long interruptible waits are generally user requested... */
 158         if (inter && usecs > 5000)
 159                 return;
 160
 161         /* Negative sleeps are time going backwards */
 162         /* Zero-time sleeps are non-interesting */
 163         if (usecs <= 0)
 164                 return;
 165
 166         memset(&lat, 0, sizeof(lat));
 167         lat.count = 1;
 168         lat.time = usecs;
 169         lat.max = usecs;
 170
 171         stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0);
 172
 173         raw_spin_lock_irqsave(&latency_lock, flags);
 174
 175         account_global_scheduler_latency(tsk, &lat);
 176
 177         for (i = 0; i < tsk->latency_record_count; i++) {
 178                 struct latency_record *mylat;
 179                 int same = 1;
 180
 181                 mylat = &tsk->latency_record[i];
 182                 for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
 183                         unsigned long record = lat.backtrace[q];
 184
 185                         if (mylat->backtrace[q] != record) {
 186                                 same = 0;
 187                                 break;
 188                         }
 189
 190                         /* 0 entry is end of backtrace */
 191                         if (!record)
 192                                 break;
 193                 }
 194                 if (same) {
 195                         mylat->count++;
 196                         mylat->time += lat.time;
 197                         if (lat.time > mylat->max)
 198                                 mylat->max = lat.time;
 199                         goto out_unlock;
 200                 }
 201         }
 202
 203         /*
 204          * short term hack; if we're > 32 we stop; future we recycle:
 205          */
 206         if (tsk->latency_record_count >= LT_SAVECOUNT)
 207                 goto out_unlock;
 208
 209         /* Allocated a new one: */
 210         i = tsk->latency_record_count++;
 211         memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record));
 212
 213 out_unlock:
 214         raw_spin_unlock_irqrestore(&latency_lock, flags);
 215 }
 216
 217 static int lstats_show(struct seq_file *m, void *v)
 218 {
 219         int i;
 220
 221         seq_puts(m, "Latency Top version : v0.1\n");
 222
 223         for (i = 0; i < MAXLR; i++) {
 224                 struct latency_record *lr = &latency_record[i];
 225
 226                 if (lr->backtrace[0]) {
 227                         int q;
 228                         seq_printf(m, "%i %lu %lu",
 229                                    lr->count, lr->time, lr->max);
 230                         for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
 231                                 unsigned long bt = lr->backtrace[q];
 232
 233                                 if (!bt)
 234                                         break;
 235
 236                                 seq_printf(m, " %ps", (void *)bt);
 237                         }
 238                         seq_puts(m, "\n");
 239                 }
 240         }
 241         return 0;
 242 }
 243
 244 static ssize_t
 245 lstats_write(struct file *file, const char __user *buf, size_t count,
 246              loff_t *offs)
 247 {
 248         clear_global_latency_tracing();
 249
 250         return count;
 251 }
 252
 253 static int lstats_open(struct inode *inode, struct file *filp)
 254 {
 255         return single_open(filp, lstats_show, NULL);
 256 }
 257
 258 static const struct proc_ops lstats_proc_ops = {
 259         .proc_open      = lstats_open,
 260         .proc_read      = seq_read,
 261         .proc_write     = lstats_write,
 262         .proc_lseek     = seq_lseek,
 263         .proc_release   = single_release,
 264 };
 265
 266 static int __init init_lstats_procfs(void)
 267 {
 268         proc_create("latency_stats", 0644, NULL, &lstats_proc_ops);
 269         return 0;
 270 }
 271
 272 int sysctl_latencytop(struct ctl_table *table, int write, void *buffer,
 273                 size_t *lenp, loff_t *ppos)
 274 {
 275         int err;
 276
 277         err = proc_dointvec(table, write, buffer, lenp, ppos);
 278         if (latencytop_enabled)
 279                 force_schedstat_enabled();
 280
 281         return err;
 282 }
 283 device_initcall(init_lstats_procfs);