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