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 /* For the CLR_() macros */
  12 #include <pthread.h>
  13
  14 #include <signal.h>
  15 #include "../util/stat.h"
  16 #include <subcmd/parse-options.h>
  17 #include <linux/compiler.h>
  18 #include <linux/kernel.h>
  19 #include <errno.h>
  20 #include "bench.h"
  21 #include "futex.h"
  22
  23 #include <err.h>
  24 #include <stdlib.h>
  25 #include <sys/time.h>
  26
  27 /* all threads will block on the same futex */
  28 static u_int32_t futex1 = 0;
  29
  30 /*
  31  * How many wakeups to do at a time.
  32  * Default to 1 in order to make the kernel work more.
  33  */
  34 static unsigned int nwakes = 1;
  35
  36 pthread_t *worker;
  37 static bool done = false, silent = false, fshared = false;
  38 static pthread_mutex_t thread_lock;
  39 static pthread_cond_t thread_parent, thread_worker;
  40 static struct stats waketime_stats, wakeup_stats;
  41 static unsigned int ncpus, threads_starting, nthreads = 0;
  42 static int futex_flag = 0;
  43
  44 static const struct option options[] = {
  45         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
  46         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
  47         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  48         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  49         OPT_END()
  50 };
  51
  52 static const char * const bench_futex_wake_usage[] = {
  53         "perf bench futex wake <options>",
  54         NULL
  55 };
  56
  57 static void *workerfn(void *arg __maybe_unused)
  58 {
  59         pthread_mutex_lock(&thread_lock);
  60         threads_starting--;
  61         if (!threads_starting)
  62                 pthread_cond_signal(&thread_parent);
  63         pthread_cond_wait(&thread_worker, &thread_lock);
  64         pthread_mutex_unlock(&thread_lock);
  65
  66         while (1) {
  67                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
  68                         break;
  69         }
  70
  71         pthread_exit(NULL);
  72         return NULL;
  73 }
  74
  75 static void print_summary(void)
  76 {
  77         double waketime_avg = avg_stats(&waketime_stats);
  78         double waketime_stddev = stddev_stats(&waketime_stats);
  79         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  80
  81         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  82                wakeup_avg,
  83                nthreads,
  84                waketime_avg/1e3,
  85                rel_stddev_stats(waketime_stddev, waketime_avg));
  86 }
  87
  88 static void block_threads(pthread_t *w,
  89                           pthread_attr_t thread_attr)
  90 {
  91         cpu_set_t cpu;
  92         unsigned int i;
  93
  94         threads_starting = nthreads;
  95
  96         /* create and block all threads */
  97         for (i = 0; i < nthreads; i++) {
  98                 CPU_ZERO(&cpu);
  99                 CPU_SET(i % ncpus, &cpu);
 100
 101                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
 102                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 103
 104                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 105                         err(EXIT_FAILURE, "pthread_create");
 106         }
 107 }
 108
 109 static void toggle_done(int sig __maybe_unused,
 110                         siginfo_t *info __maybe_unused,
 111                         void *uc __maybe_unused)
 112 {
 113         done = true;
 114 }
 115
 116 int bench_futex_wake(int argc, const char **argv,
 117                      const char *prefix __maybe_unused)
 118 {
 119         int ret = 0;
 120         unsigned int i, j;
 121         struct sigaction act;
 122         pthread_attr_t thread_attr;
 123
 124         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 125         if (argc) {
 126                 usage_with_options(bench_futex_wake_usage, options);
 127                 exit(EXIT_FAILURE);
 128         }
 129
 130         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 131
 132         sigfillset(&act.sa_mask);
 133         act.sa_sigaction = toggle_done;
 134         sigaction(SIGINT, &act, NULL);
 135
 136         if (!nthreads)
 137                 nthreads = ncpus;
 138
 139         worker = calloc(nthreads, sizeof(*worker));
 140         if (!worker)
 141                 err(EXIT_FAILURE, "calloc");
 142
 143         if (!fshared)
 144                 futex_flag = FUTEX_PRIVATE_FLAG;
 145
 146         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 147                "waking up %d at a time.\n\n",
 148                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
 149
 150         init_stats(&wakeup_stats);
 151         init_stats(&waketime_stats);
 152         pthread_attr_init(&thread_attr);
 153         pthread_mutex_init(&thread_lock, NULL);
 154         pthread_cond_init(&thread_parent, NULL);
 155         pthread_cond_init(&thread_worker, NULL);
 156
 157         for (j = 0; j < bench_repeat && !done; j++) {
 158                 unsigned int nwoken = 0;
 159                 struct timeval start, end, runtime;
 160
 161                 /* create, launch & block all threads */
 162                 block_threads(worker, thread_attr);
 163
 164                 /* make sure all threads are already blocked */
 165                 pthread_mutex_lock(&thread_lock);
 166                 while (threads_starting)
 167                         pthread_cond_wait(&thread_parent, &thread_lock);
 168                 pthread_cond_broadcast(&thread_worker);
 169                 pthread_mutex_unlock(&thread_lock);
 170
 171                 usleep(100000);
 172
 173                 /* Ok, all threads are patiently blocked, start waking folks up */
 174                 gettimeofday(&start, NULL);
 175                 while (nwoken != nthreads)
 176                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
 177                 gettimeofday(&end, NULL);
 178                 timersub(&end, &start, &runtime);
 179
 180                 update_stats(&wakeup_stats, nwoken);
 181                 update_stats(&waketime_stats, runtime.tv_usec);
 182
 183                 if (!silent) {
 184                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 185                                j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
 186                 }
 187
 188                 for (i = 0; i < nthreads; i++) {
 189                         ret = pthread_join(worker[i], NULL);
 190                         if (ret)
 191                                 err(EXIT_FAILURE, "pthread_join");
 192                 }
 193
 194         }
 195
 196         /* cleanup & report results */
 197         pthread_cond_destroy(&thread_parent);
 198         pthread_cond_destroy(&thread_worker);
 199         pthread_mutex_destroy(&thread_lock);
 200         pthread_attr_destroy(&thread_attr);
 201
 202         print_summary();
 203
 204         free(worker);
 205         return ret;
 206 }