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, 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         futex_wait(&futex1, 0, NULL, futex_flag);
  64         return NULL;
  65 }
  66
  67 static void print_summary(void)
  68 {
  69         double waketime_avg = avg_stats(&waketime_stats);
  70         double waketime_stddev = stddev_stats(&waketime_stats);
  71         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  72
  73         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  74                wakeup_avg,
  75                nthreads,
  76                waketime_avg/1e3,
  77                rel_stddev_stats(waketime_stddev, waketime_avg));
  78 }
  79
  80 static void block_threads(pthread_t *w,
  81                           pthread_attr_t thread_attr)
  82 {
  83         cpu_set_t cpu;
  84         unsigned int i;
  85
  86         threads_starting = nthreads;
  87
  88         /* create and block all threads */
  89         for (i = 0; i < nthreads; i++) {
  90                 CPU_ZERO(&cpu);
  91                 CPU_SET(i % ncpus, &cpu);
  92
  93                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
  94                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
  95
  96                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
  97                         err(EXIT_FAILURE, "pthread_create");
  98         }
  99 }
 100
 101 static void toggle_done(int sig __maybe_unused,
 102                         siginfo_t *info __maybe_unused,
 103                         void *uc __maybe_unused)
 104 {
 105         done = true;
 106 }
 107
 108 int bench_futex_wake(int argc, const char **argv,
 109                      const char *prefix __maybe_unused)
 110 {
 111         int ret = 0;
 112         unsigned int i, j;
 113         struct sigaction act;
 114         pthread_attr_t thread_attr;
 115
 116         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 117         if (argc) {
 118                 usage_with_options(bench_futex_wake_usage, options);
 119                 exit(EXIT_FAILURE);
 120         }
 121
 122         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 123
 124         sigfillset(&act.sa_mask);
 125         act.sa_sigaction = toggle_done;
 126         sigaction(SIGINT, &act, NULL);
 127
 128         if (!nthreads)
 129                 nthreads = ncpus;
 130
 131         worker = calloc(nthreads, sizeof(*worker));
 132         if (!worker)
 133                 err(EXIT_FAILURE, "calloc");
 134
 135         if (!fshared)
 136                 futex_flag = FUTEX_PRIVATE_FLAG;
 137
 138         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 139                "waking up %d at a time.\n\n",
 140                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
 141
 142         init_stats(&wakeup_stats);
 143         init_stats(&waketime_stats);
 144         pthread_attr_init(&thread_attr);
 145         pthread_mutex_init(&thread_lock, NULL);
 146         pthread_cond_init(&thread_parent, NULL);
 147         pthread_cond_init(&thread_worker, NULL);
 148
 149         for (j = 0; j < bench_repeat && !done; j++) {
 150                 unsigned int nwoken = 0;
 151                 struct timeval start, end, runtime;
 152
 153                 /* create, launch & block all threads */
 154                 block_threads(worker, thread_attr);
 155
 156                 /* make sure all threads are already blocked */
 157                 pthread_mutex_lock(&thread_lock);
 158                 while (threads_starting)
 159                         pthread_cond_wait(&thread_parent, &thread_lock);
 160                 pthread_cond_broadcast(&thread_worker);
 161                 pthread_mutex_unlock(&thread_lock);
 162
 163                 usleep(100000);
 164
 165                 /* Ok, all threads are patiently blocked, start waking folks up */
 166                 gettimeofday(&start, NULL);
 167                 while (nwoken != nthreads)
 168                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
 169                 gettimeofday(&end, NULL);
 170                 timersub(&end, &start, &runtime);
 171
 172                 update_stats(&wakeup_stats, nwoken);
 173                 update_stats(&waketime_stats, runtime.tv_usec);
 174
 175                 if (!silent) {
 176                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 177                                j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
 178                 }
 179
 180                 for (i = 0; i < nthreads; i++) {
 181                         ret = pthread_join(worker[i], NULL);
 182                         if (ret)
 183                                 err(EXIT_FAILURE, "pthread_join");
 184                 }
 185
 186         }
 187
 188         /* cleanup & report results */
 189         pthread_cond_destroy(&thread_parent);
 190         pthread_cond_destroy(&thread_worker);
 191         pthread_mutex_destroy(&thread_lock);
 192         pthread_attr_destroy(&thread_attr);
 193
 194         print_summary();
 195
 196         free(worker);
 197         return ret;
 198 }