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 "bench.h"
  24 #include "futex.h"
  25 #include "cpumap.h"
  26
  27 #include <err.h>
  28 #include <stdlib.h>
  29 #include <sys/time.h>
  30
  31 /* all threads will block on the same futex */
  32 static u_int32_t futex1 = 0;
  33
  34 /*
  35  * How many wakeups to do at a time.
  36  * Default to 1 in order to make the kernel work more.
  37  */
  38 static unsigned int nwakes = 1;
  39
  40 pthread_t *worker;
  41 static bool done = false, silent = false, fshared = false;
  42 static pthread_mutex_t thread_lock;
  43 static pthread_cond_t thread_parent, thread_worker;
  44 static struct stats waketime_stats, wakeup_stats;
  45 static unsigned int threads_starting, nthreads = 0;
  46 static int futex_flag = 0;
  47
  48 static const struct option options[] = {
  49         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
  50         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
  51         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
  52         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
  53         OPT_END()
  54 };
  55
  56 static const char * const bench_futex_wake_usage[] = {
  57         "perf bench futex wake <options>",
  58         NULL
  59 };
  60
  61 static void *workerfn(void *arg __maybe_unused)
  62 {
  63         pthread_mutex_lock(&thread_lock);
  64         threads_starting--;
  65         if (!threads_starting)
  66                 pthread_cond_signal(&thread_parent);
  67         pthread_cond_wait(&thread_worker, &thread_lock);
  68         pthread_mutex_unlock(&thread_lock);
  69
  70         while (1) {
  71                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
  72                         break;
  73         }
  74
  75         pthread_exit(NULL);
  76         return NULL;
  77 }
  78
  79 static void print_summary(void)
  80 {
  81         double waketime_avg = avg_stats(&waketime_stats);
  82         double waketime_stddev = stddev_stats(&waketime_stats);
  83         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
  84
  85         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
  86                wakeup_avg,
  87                nthreads,
  88                waketime_avg / USEC_PER_MSEC,
  89                rel_stddev_stats(waketime_stddev, waketime_avg));
  90 }
  91
  92 static void block_threads(pthread_t *w,
  93                           pthread_attr_t thread_attr, struct cpu_map *cpu)
  94 {
  95         cpu_set_t cpuset;
  96         unsigned int i;
  97
  98         threads_starting = nthreads;
  99
 100         /* create and block all threads */
 101         for (i = 0; i < nthreads; i++) {
 102                 CPU_ZERO(&cpuset);
 103                 CPU_SET(cpu->map[i % cpu->nr], &cpuset);
 104
 105                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
 106                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 107
 108                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 109                         err(EXIT_FAILURE, "pthread_create");
 110         }
 111 }
 112
 113 static void toggle_done(int sig __maybe_unused,
 114                         siginfo_t *info __maybe_unused,
 115                         void *uc __maybe_unused)
 116 {
 117         done = true;
 118 }
 119
 120 int bench_futex_wake(int argc, const char **argv)
 121 {
 122         int ret = 0;
 123         unsigned int i, j;
 124         struct sigaction act;
 125         pthread_attr_t thread_attr;
 126         struct cpu_map *cpu;
 127
 128         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
 129         if (argc) {
 130                 usage_with_options(bench_futex_wake_usage, options);
 131                 exit(EXIT_FAILURE);
 132         }
 133
 134         cpu = cpu_map__new(NULL);
 135         if (!cpu)
 136                 err(EXIT_FAILURE, "calloc");
 137
 138         sigfillset(&act.sa_mask);
 139         act.sa_sigaction = toggle_done;
 140         sigaction(SIGINT, &act, NULL);
 141
 142         if (!nthreads)
 143                 nthreads = cpu->nr;
 144
 145         worker = calloc(nthreads, sizeof(*worker));
 146         if (!worker)
 147                 err(EXIT_FAILURE, "calloc");
 148
 149         if (!fshared)
 150                 futex_flag = FUTEX_PRIVATE_FLAG;
 151
 152         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
 153                "waking up %d at a time.\n\n",
 154                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
 155
 156         init_stats(&wakeup_stats);
 157         init_stats(&waketime_stats);
 158         pthread_attr_init(&thread_attr);
 159         pthread_mutex_init(&thread_lock, NULL);
 160         pthread_cond_init(&thread_parent, NULL);
 161         pthread_cond_init(&thread_worker, NULL);
 162
 163         for (j = 0; j < bench_repeat && !done; j++) {
 164                 unsigned int nwoken = 0;
 165                 struct timeval start, end, runtime;
 166
 167                 /* create, launch & block all threads */
 168                 block_threads(worker, thread_attr, cpu);
 169
 170                 /* make sure all threads are already blocked */
 171                 pthread_mutex_lock(&thread_lock);
 172                 while (threads_starting)
 173                         pthread_cond_wait(&thread_parent, &thread_lock);
 174                 pthread_cond_broadcast(&thread_worker);
 175                 pthread_mutex_unlock(&thread_lock);
 176
 177                 usleep(100000);
 178
 179                 /* Ok, all threads are patiently blocked, start waking folks up */
 180                 gettimeofday(&start, NULL);
 181                 while (nwoken != nthreads)
 182                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
 183                 gettimeofday(&end, NULL);
 184                 timersub(&end, &start, &runtime);
 185
 186                 update_stats(&wakeup_stats, nwoken);
 187                 update_stats(&waketime_stats, runtime.tv_usec);
 188
 189                 if (!silent) {
 190                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
 191                                j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
 192                 }
 193
 194                 for (i = 0; i < nthreads; i++) {
 195                         ret = pthread_join(worker[i], NULL);
 196                         if (ret)
 197                                 err(EXIT_FAILURE, "pthread_join");
 198                 }
 199
 200         }
 201
 202         /* cleanup & report results */
 203         pthread_cond_destroy(&thread_parent);
 204         pthread_cond_destroy(&thread_worker);
 205         pthread_mutex_destroy(&thread_lock);
 206         pthread_attr_destroy(&thread_attr);
 207
 208         print_summary();
 209
 210         free(worker);
 211         return ret;
 212 }