tools/perf/bench/futex-wake.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   4  *
   5  * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
   6  *
   7  * This program is particularly useful to measure the latency of nthread wakeups
   8  * in non-error situations:  all waiters are queued and all wake calls wakeup
   9  * one or more tasks, and thus the waitqueue is never empty.
  10  */
  11
  12 /* For the CLR_() macros */
  13 #include <string.h>
  14 #include <pthread.h>
  15
  16 #include <signal.h>
  17 #include "../util/stat.h"
  18 #include <subcmd/parse-options.h>
  19 #include <linux/compiler.h>
  20 #include <linux/kernel.h>
  21 #include <linux/time64.h>
  22 #include <errno.h>
  23 #include <internal/cpumap.h>
  24 #include <perf/cpumap.h>
  25 #include "bench.h"
  26 #include "futex.h"
  27
  28 #include <err.h>
  29 #include <stdlib.h>
  30 #include <sys/time.h>
  31
  32 /* all threads will block on the same futex */
  33 static u_int32_t futex1 = 0;
  34
  35 /*
  36  * How many wakeups to do at a time.
  37  * Default to 1 in order to make the kernel work more.
  38  */
  39 static unsigned int nwakes = 1;
  40
  41 pthread_t *worker;
  42 static bool done = false, silent = false, fshared = false;
  43 static pthread_mutex_t thread_lock;
  44 static pthread_cond_t thread_parent, thread_worker;
  45 static struct stats waketime_stats, wakeup_stats;
  46 static unsigned int threads_starting, nthreads = 0;
  47 static int futex_flag = 0;
  48
  49 static const struct option options[] = {
  50         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
  51         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
  52         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  53         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  54         OPT_END()
  55 };
  56
  57 static const char * const bench_futex_wake_usage[] = {
  58         "perf bench futex wake <options>",
  59         NULL
  60 };
  61
  62 static void *workerfn(void *arg __maybe_unused)
  63 {
  64         pthread_mutex_lock(&thread_lock);
  65         threads_starting--;
  66         if (!threads_starting)
  67                 pthread_cond_signal(&thread_parent);
  68         pthread_cond_wait(&thread_worker, &thread_lock);
  69         pthread_mutex_unlock(&thread_lock);
  70
  71         while (1) {
  72                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
  73                         break;
  74         }
  75
  76         pthread_exit(NULL);
  77         return NULL;
  78 }
  79
  80 static void print_summary(void)
  81 {
  82         double waketime_avg = avg_stats(&waketime_stats);
  83         double waketime_stddev = stddev_stats(&waketime_stats);
  84         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  85
  86         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  87                wakeup_avg,
  88                nthreads,
  89                waketime_avg / USEC_PER_MSEC,
  90                rel_stddev_stats(waketime_stddev, waketime_avg));
  91 }
  92
  93 static void block_threads(pthread_t *w,
  94                           pthread_attr_t thread_attr, struct perf_cpu_map *cpu)
  95 {
  96         cpu_set_t cpuset;
  97         unsigned int i;
  98
  99         threads_starting = nthreads;
 100
 101         /* create and block all threads */
 102         for (i = 0; i < nthreads; i++) {
 103                 CPU_ZERO(&cpuset);
 104                 CPU_SET(cpu->map[i % cpu->nr], &cpuset);
 105
 106                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
 107                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 108
 109                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 110                         err(EXIT_FAILURE, "pthread_create");
 111         }
 112 }
 113
 114 static void toggle_done(int sig __maybe_unused,
 115                         siginfo_t *info __maybe_unused,
 116                         void *uc __maybe_unused)
 117 {
 118         done = true;
 119 }
 120
 121 int bench_futex_wake(int argc, const char **argv)
 122 {
 123         int ret = 0;
 124         unsigned int i, j;
 125         struct sigaction act;
 126         pthread_attr_t thread_attr;
 127         struct perf_cpu_map *cpu;
 128
 129         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 130         if (argc) {
 131                 usage_with_options(bench_futex_wake_usage, options);
 132                 exit(EXIT_FAILURE);
 133         }
 134
 135         cpu = perf_cpu_map__new(NULL);
 136         if (!cpu)
 137                 err(EXIT_FAILURE, "calloc");
 138
 139         sigfillset(&act.sa_mask);
 140         act.sa_sigaction = toggle_done;
 141         sigaction(SIGINT, &act, NULL);
 142
 143         if (!nthreads)
 144                 nthreads = cpu->nr;
 145
 146         worker = calloc(nthreads, sizeof(*worker));
 147         if (!worker)
 148                 err(EXIT_FAILURE, "calloc");
 149
 150         if (!fshared)
 151                 futex_flag = FUTEX_PRIVATE_FLAG;
 152
 153         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 154                "waking up %d at a time.\n\n",
 155                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
 156
 157         init_stats(&wakeup_stats);
 158         init_stats(&waketime_stats);
 159         pthread_attr_init(&thread_attr);
 160         pthread_mutex_init(&thread_lock, NULL);
 161         pthread_cond_init(&thread_parent, NULL);
 162         pthread_cond_init(&thread_worker, NULL);
 163
 164         for (j = 0; j < bench_repeat && !done; j++) {
 165                 unsigned int nwoken = 0;
 166                 struct timeval start, end, runtime;
 167
 168                 /* create, launch & block all threads */
 169                 block_threads(worker, thread_attr, cpu);
 170
 171                 /* make sure all threads are already blocked */
 172                 pthread_mutex_lock(&thread_lock);
 173                 while (threads_starting)
 174                         pthread_cond_wait(&thread_parent, &thread_lock);
 175                 pthread_cond_broadcast(&thread_worker);
 176                 pthread_mutex_unlock(&thread_lock);
 177
 178                 usleep(100000);
 179
 180                 /* Ok, all threads are patiently blocked, start waking folks up */
 181                 gettimeofday(&start, NULL);
 182                 while (nwoken != nthreads)
 183                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
 184                 gettimeofday(&end, NULL);
 185                 timersub(&end, &start, &runtime);
 186
 187                 update_stats(&wakeup_stats, nwoken);
 188                 update_stats(&waketime_stats, runtime.tv_usec);
 189
 190                 if (!silent) {
 191                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 192                                j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
 193                 }
 194
 195                 for (i = 0; i < nthreads; i++) {
 196                         ret = pthread_join(worker[i], NULL);
 197                         if (ret)
 198                                 err(EXIT_FAILURE, "pthread_join");
 199                 }
 200
 201         }
 202
 203         /* cleanup & report results */
 204         pthread_cond_destroy(&thread_parent);
 205         pthread_cond_destroy(&thread_worker);
 206         pthread_mutex_destroy(&thread_lock);
 207         pthread_attr_destroy(&thread_attr);
 208
 209         print_summary();
 210
 211         free(worker);
 212         return ret;
 213 }