tools/perf/bench/futex-requeue.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   4  *
   5  * futex-requeue: Block a bunch of threads on futex1 and requeue them
   6  *                on futex2, N at a time.
   7  *
   8  * This program is particularly useful to measure the latency of nthread
   9  * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
  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
  26 #include <err.h>
  27 #include <stdlib.h>
  28 #include <sys/time.h>
  29
  30 static u_int32_t futex1 = 0, futex2 = 0;
  31
  32 /*
  33  * How many tasks to requeue at a time.
  34  * Default to 1 in order to make the kernel work more.
  35  */
  36 static unsigned int nrequeue = 1;
  37
  38 static pthread_t *worker;
  39 static bool done = false, silent = false, fshared = false;
  40 static pthread_mutex_t thread_lock;
  41 static pthread_cond_t thread_parent, thread_worker;
  42 static struct stats requeuetime_stats, requeued_stats;
  43 static unsigned int ncpus, threads_starting, nthreads = 0;
  44 static int futex_flag = 0;
  45
  46 static const struct option options[] = {
  47         OPT_UINTEGER('t', "threads",  &nthreads, "Specify amount of threads"),
  48         OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue at once"),
  49         OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
  50         OPT_BOOLEAN( 'S', "shared",   &fshared,  "Use shared futexes instead of private ones"),
  51         OPT_END()
  52 };
  53
  54 static const char * const bench_futex_requeue_usage[] = {
  55         "perf bench futex requeue <options>",
  56         NULL
  57 };
  58
  59 static void print_summary(void)
  60 {
  61         double requeuetime_avg = avg_stats(&requeuetime_stats);
  62         double requeuetime_stddev = stddev_stats(&requeuetime_stats);
  63         unsigned int requeued_avg = avg_stats(&requeued_stats);
  64
  65         printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
  66                requeued_avg,
  67                nthreads,
  68                requeuetime_avg / USEC_PER_MSEC,
  69                rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
  70 }
  71
  72 static void *workerfn(void *arg __maybe_unused)
  73 {
  74         pthread_mutex_lock(&thread_lock);
  75         threads_starting--;
  76         if (!threads_starting)
  77                 pthread_cond_signal(&thread_parent);
  78         pthread_cond_wait(&thread_worker, &thread_lock);
  79         pthread_mutex_unlock(&thread_lock);
  80
  81         futex_wait(&futex1, 0, NULL, futex_flag);
  82         return NULL;
  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_requeue(int argc, const char **argv)
 114 {
 115         int ret = 0;
 116         unsigned int i, j;
 117         struct sigaction act;
 118         pthread_attr_t thread_attr;
 119
 120         argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
 121         if (argc)
 122                 goto err;
 123
 124         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 125
 126         sigfillset(&act.sa_mask);
 127         act.sa_sigaction = toggle_done;
 128         sigaction(SIGINT, &act, NULL);
 129
 130         if (!nthreads)
 131                 nthreads = ncpus;
 132
 133         worker = calloc(nthreads, sizeof(*worker));
 134         if (!worker)
 135                 err(EXIT_FAILURE, "calloc");
 136
 137         if (!fshared)
 138                 futex_flag = FUTEX_PRIVATE_FLAG;
 139
 140         if (nrequeue > nthreads)
 141                 nrequeue = nthreads;
 142
 143         printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
 144                "%d at a time.\n\n",  getpid(), nthreads,
 145                fshared ? "shared":"private", &futex1, &futex2, nrequeue);
 146
 147         init_stats(&requeued_stats);
 148         init_stats(&requeuetime_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 nrequeued = 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 requeueing */
 171                 gettimeofday(&start, NULL);
 172                 while (nrequeued < nthreads) {
 173                         /*
 174                          * Do not wakeup any tasks blocked on futex1, allowing
 175                          * us to really measure futex_wait functionality.
 176                          */
 177                         nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
 178                                                        nrequeue, futex_flag);
 179                 }
 180
 181                 gettimeofday(&end, NULL);
 182                 timersub(&end, &start, &runtime);
 183
 184                 update_stats(&requeued_stats, nrequeued);
 185                 update_stats(&requeuetime_stats, runtime.tv_usec);
 186
 187                 if (!silent) {
 188                         printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
 189                                j + 1, nrequeued, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
 190                 }
 191
 192                 /* everybody should be blocked on futex2, wake'em up */
 193                 nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
 194                 if (nthreads != nrequeued)
 195                         warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
 196
 197                 for (i = 0; i < nthreads; i++) {
 198                         ret = pthread_join(worker[i], NULL);
 199                         if (ret)
 200                                 err(EXIT_FAILURE, "pthread_join");
 201                 }
 202         }
 203
 204         /* cleanup & report results */
 205         pthread_cond_destroy(&thread_parent);
 206         pthread_cond_destroy(&thread_worker);
 207         pthread_mutex_destroy(&thread_lock);
 208         pthread_attr_destroy(&thread_attr);
 209
 210         print_summary();
 211
 212         free(worker);
 213         return ret;
 214 err:
 215         usage_with_options(bench_futex_requeue_usage, options);
 216         exit(EXIT_FAILURE);
 217 }