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