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