tools/perf/bench/futex-wake.c

   1 /*
   2  * Copyright (C) 2013  Davidlohr Bueso <[email protected]>
   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 <string.h>
  13 #include <pthread.h>
  14
  15 #include <signal.h>
  16 #include "../util/stat.h"
  17 #include <subcmd/parse-options.h>
  18 #include <linux/compiler.h>
  19 #include <linux/kernel.h>
  20 #include <linux/time64.h>
  21 #include <errno.h>
  22 #include "bench.h"
  23 #include "futex.h"
  24
  25 #include <err.h>
  26 #include <stdlib.h>
  27 #include <sys/time.h>
  28
  29 /* all threads will block on the same futex */
  30 static u_int32_t futex1 = 0;
  31
  32 /*
  33  * How many wakeups to do at a time.
  34  * Default to 1 in order to make the kernel work more.
  35  */
  36 static unsigned int nwakes = 1;
  37
  38 pthread_t *worker;
  39 static bool done = false, silent = false, fshared = false;
  40 static pthread_mutex_t thread_lock;
  41 static pthread_cond_t thread_parent, thread_worker;
  42 static struct stats waketime_stats, wakeup_stats;
  43 static unsigned int ncpus, threads_starting, nthreads = 0;
  44 static int futex_flag = 0;
  45
  46 static const struct option options[] = {
  47         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
  48         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
  49         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  50         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  51         OPT_END()
  52 };
  53
  54 static const char * const bench_futex_wake_usage[] = {
  55         "perf bench futex wake <options>",
  56         NULL
  57 };
  58
  59 static void *workerfn(void *arg __maybe_unused)
  60 {
  61         pthread_mutex_lock(&thread_lock);
  62         threads_starting--;
  63         if (!threads_starting)
  64                 pthread_cond_signal(&thread_parent);
  65         pthread_cond_wait(&thread_worker, &thread_lock);
  66         pthread_mutex_unlock(&thread_lock);
  67
  68         while (1) {
  69                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
  70                         break;
  71         }
  72
  73         pthread_exit(NULL);
  74         return NULL;
  75 }
  76
  77 static void print_summary(void)
  78 {
  79         double waketime_avg = avg_stats(&waketime_stats);
  80         double waketime_stddev = stddev_stats(&waketime_stats);
  81         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  82
  83         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  84                wakeup_avg,
  85                nthreads,
  86                waketime_avg / USEC_PER_MSEC,
  87                rel_stddev_stats(waketime_stddev, waketime_avg));
  88 }
  89
  90 static void block_threads(pthread_t *w,
  91                           pthread_attr_t thread_attr)
  92 {
  93         cpu_set_t cpu;
  94         unsigned int i;
  95
  96         threads_starting = nthreads;
  97
  98         /* create and block all threads */
  99         for (i = 0; i < nthreads; i++) {
 100                 CPU_ZERO(&cpu);
 101                 CPU_SET(i % ncpus, &cpu);
 102
 103                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
 104                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 105
 106                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 107                         err(EXIT_FAILURE, "pthread_create");
 108         }
 109 }
 110
 111 static void toggle_done(int sig __maybe_unused,
 112                         siginfo_t *info __maybe_unused,
 113                         void *uc __maybe_unused)
 114 {
 115         done = true;
 116 }
 117
 118 int bench_futex_wake(int argc, const char **argv)
 119 {
 120         int ret = 0;
 121         unsigned int i, j;
 122         struct sigaction act;
 123         pthread_attr_t thread_attr;
 124
 125         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 126         if (argc) {
 127                 usage_with_options(bench_futex_wake_usage, options);
 128                 exit(EXIT_FAILURE);
 129         }
 130
 131         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 132
 133         sigfillset(&act.sa_mask);
 134         act.sa_sigaction = toggle_done;
 135         sigaction(SIGINT, &act, NULL);
 136
 137         if (!nthreads)
 138                 nthreads = ncpus;
 139
 140         worker = calloc(nthreads, sizeof(*worker));
 141         if (!worker)
 142                 err(EXIT_FAILURE, "calloc");
 143
 144         if (!fshared)
 145                 futex_flag = FUTEX_PRIVATE_FLAG;
 146
 147         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 148                "waking up %d at a time.\n\n",
 149                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
 150
 151         init_stats(&wakeup_stats);
 152         init_stats(&waketime_stats);
 153         pthread_attr_init(&thread_attr);
 154         pthread_mutex_init(&thread_lock, NULL);
 155         pthread_cond_init(&thread_parent, NULL);
 156         pthread_cond_init(&thread_worker, NULL);
 157
 158         for (j = 0; j < bench_repeat && !done; j++) {
 159                 unsigned int nwoken = 0;
 160                 struct timeval start, end, runtime;
 161
 162                 /* create, launch & block all threads */
 163                 block_threads(worker, thread_attr);
 164
 165                 /* make sure all threads are already blocked */
 166                 pthread_mutex_lock(&thread_lock);
 167                 while (threads_starting)
 168                         pthread_cond_wait(&thread_parent, &thread_lock);
 169                 pthread_cond_broadcast(&thread_worker);
 170                 pthread_mutex_unlock(&thread_lock);
 171
 172                 usleep(100000);
 173
 174                 /* Ok, all threads are patiently blocked, start waking folks up */
 175                 gettimeofday(&start, NULL);
 176                 while (nwoken != nthreads)
 177                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
 178                 gettimeofday(&end, NULL);
 179                 timersub(&end, &start, &runtime);
 180
 181                 update_stats(&wakeup_stats, nwoken);
 182                 update_stats(&waketime_stats, runtime.tv_usec);
 183
 184                 if (!silent) {
 185                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 186                                j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
 187                 }
 188
 189                 for (i = 0; i < nthreads; i++) {
 190                         ret = pthread_join(worker[i], NULL);
 191                         if (ret)
 192                                 err(EXIT_FAILURE, "pthread_join");
 193                 }
 194
 195         }
 196
 197         /* cleanup & report results */
 198         pthread_cond_destroy(&thread_parent);
 199         pthread_cond_destroy(&thread_worker);
 200         pthread_mutex_destroy(&thread_lock);
 201         pthread_attr_destroy(&thread_attr);
 202
 203         print_summary();
 204
 205         free(worker);
 206         return ret;
 207 }