tools/perf/bench/futex-wake.c

   1 /*
   2  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   3  *
   4  * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
   5  *
   6  * This program is particularly useful to measure the latency of nthread wakeups
   7  * in non-error situations:  all waiters are queued and all wake calls wakeup
   8  * one or more tasks, and thus the waitqueue is never empty.
   9  */
  10
  11 #include "../perf.h"
  12 #include "../util/util.h"
  13 #include "../util/stat.h"
  14 #include "../util/parse-options.h"
  15 #include "../util/header.h"
  16 #include "bench.h"
  17 #include "futex.h"
  18
  19 #include <err.h>
  20 #include <stdlib.h>
  21 #include <sys/time.h>
  22 #include <pthread.h>
  23
  24 /* all threads will block on the same futex */
  25 static u_int32_t futex1 = 0;
  26
  27 /*
  28  * How many wakeups to do at a time.
  29  * Default to 1 in order to make the kernel work more.
  30  */
  31 static unsigned int nwakes = 1;
  32
  33 /*
  34  * There can be significant variance from run to run,
  35  * the more repeats, the more exact the overall avg and
  36  * the better idea of the futex latency.
  37  */
  38 static unsigned int repeat = 10;
  39
  40 pthread_t *worker;
  41 static bool done = 0, silent = 0;
  42 static pthread_mutex_t thread_lock;
  43 static pthread_cond_t thread_parent, thread_worker;
  44 static struct stats waketime_stats, wakeup_stats;
  45 static unsigned int ncpus, threads_starting, nthreads = 0;
  46
  47 static const struct option options[] = {
  48         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
  49         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
  50         OPT_UINTEGER('r', "repeat",  &repeat,   "Specify amount of times to repeat the run"),
  51         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  52         OPT_END()
  53 };
  54
  55 static const char * const bench_futex_wake_usage[] = {
  56         "perf bench futex wake <options>",
  57         NULL
  58 };
  59
  60 static void *workerfn(void *arg __maybe_unused)
  61 {
  62         pthread_mutex_lock(&thread_lock);
  63         threads_starting--;
  64         if (!threads_starting)
  65                 pthread_cond_signal(&thread_parent);
  66         pthread_cond_wait(&thread_worker, &thread_lock);
  67         pthread_mutex_unlock(&thread_lock);
  68
  69         futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
  70         return NULL;
  71 }
  72
  73 static void print_summary(void)
  74 {
  75         double waketime_avg = avg_stats(&waketime_stats);
  76         double waketime_stddev = stddev_stats(&waketime_stats);
  77         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  78
  79         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  80                wakeup_avg,
  81                nthreads,
  82                waketime_avg/1e3,
  83                rel_stddev_stats(waketime_stddev, waketime_avg));
  84 }
  85
  86 static void block_threads(pthread_t *w,
  87                           pthread_attr_t thread_attr)
  88 {
  89         cpu_set_t cpu;
  90         unsigned int i;
  91
  92         threads_starting = nthreads;
  93
  94         /* create and block all threads */
  95         for (i = 0; i < nthreads; i++) {
  96                 CPU_ZERO(&cpu);
  97                 CPU_SET(i % ncpus, &cpu);
  98
  99                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
 100                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 101
 102                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 103                         err(EXIT_FAILURE, "pthread_create");
 104         }
 105 }
 106
 107 static void toggle_done(int sig __maybe_unused,
 108                         siginfo_t *info __maybe_unused,
 109                         void *uc __maybe_unused)
 110 {
 111         done = true;
 112 }
 113
 114 int bench_futex_wake(int argc, const char **argv,
 115                      const char *prefix __maybe_unused)
 116 {
 117         int ret = 0;
 118         unsigned int i, j;
 119         struct sigaction act;
 120         pthread_attr_t thread_attr;
 121
 122         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 123         if (argc) {
 124                 usage_with_options(bench_futex_wake_usage, options);
 125                 exit(EXIT_FAILURE);
 126         }
 127
 128         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 129
 130         sigfillset(&act.sa_mask);
 131         act.sa_sigaction = toggle_done;
 132         sigaction(SIGINT, &act, NULL);
 133
 134         if (!nthreads)
 135                 nthreads = ncpus;
 136
 137         worker = calloc(nthreads, sizeof(*worker));
 138         if (!worker)
 139                 err(EXIT_FAILURE, "calloc");
 140
 141         printf("Run summary [PID %d]: blocking on %d threads (at futex %p), "
 142                "waking up %d at a time.\n\n",
 143                getpid(), nthreads, &futex1, nwakes);
 144
 145         init_stats(&wakeup_stats);
 146         init_stats(&waketime_stats);
 147         pthread_attr_init(&thread_attr);
 148         pthread_mutex_init(&thread_lock, NULL);
 149         pthread_cond_init(&thread_parent, NULL);
 150         pthread_cond_init(&thread_worker, NULL);
 151
 152         for (j = 0; j < repeat && !done; j++) {
 153                 unsigned int nwoken = 0;
 154                 struct timeval start, end, runtime;
 155
 156                 /* create, launch & block all threads */
 157                 block_threads(worker, thread_attr);
 158
 159                 /* make sure all threads are already blocked */
 160                 pthread_mutex_lock(&thread_lock);
 161                 while (threads_starting)
 162                         pthread_cond_wait(&thread_parent, &thread_lock);
 163                 pthread_cond_broadcast(&thread_worker);
 164                 pthread_mutex_unlock(&thread_lock);
 165
 166                 usleep(100000);
 167
 168                 /* Ok, all threads are patiently blocked, start waking folks up */
 169                 gettimeofday(&start, NULL);
 170                 while (nwoken != nthreads)
 171                         nwoken += futex_wake(&futex1, nwakes, FUTEX_PRIVATE_FLAG);
 172                 gettimeofday(&end, NULL);
 173                 timersub(&end, &start, &runtime);
 174
 175                 update_stats(&wakeup_stats, nwoken);
 176                 update_stats(&waketime_stats, runtime.tv_usec);
 177
 178                 if (!silent) {
 179                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 180                                j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
 181                 }
 182
 183                 for (i = 0; i < nthreads; i++) {
 184                         ret = pthread_join(worker[i], NULL);
 185                         if (ret)
 186                                 err(EXIT_FAILURE, "pthread_join");
 187                 }
 188
 189         }
 190
 191         /* cleanup & report results */
 192         pthread_cond_destroy(&thread_parent);
 193         pthread_cond_destroy(&thread_worker);
 194         pthread_mutex_destroy(&thread_lock);
 195         pthread_attr_destroy(&thread_attr);
 196
 197         print_summary();
 198
 199         free(worker);
 200         return ret;
 201 }