tools/perf/bench/futex-requeue.c

   1 /*
   2  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
   3  *
   4  * futex-requeue: Block a bunch of threads on futex1 and requeue them
   5  *                on futex2, N at a time.
   6  *
   7  * This program is particularly useful to measure the latency of nthread
   8  * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
   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 static u_int32_t futex1 = 0, futex2 = 0;
  25
  26 /*
  27  * How many tasks to requeue at a time.
  28  * Default to 1 in order to make the kernel work more.
  29  */
  30 static unsigned int nrequeue = 1;
  31
  32 /*
  33  * There can be significant variance from run to run,
  34  * the more repeats, the more exact the overall avg and
  35  * the better idea of the futex latency.
  36  */
  37 static unsigned int repeat = 10;
  38
  39 static pthread_t *worker;
  40 static bool done = 0, silent = 0;
  41 static pthread_mutex_t thread_lock;
  42 static pthread_cond_t thread_parent, thread_worker;
  43 static struct stats requeuetime_stats, requeued_stats;
  44 static unsigned int ncpus, threads_starting, nthreads = 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_UINTEGER('r', "repeat",   &repeat,   "Specify amount of times to repeat the run"),
  50         OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
  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/1e3,
  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_PRIVATE_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                         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_requeue_usage, 0);
 122         if (argc)
 123                 goto err;
 124
 125         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
 126
 127         sigfillset(&act.sa_mask);
 128         act.sa_sigaction = toggle_done;
 129         sigaction(SIGINT, &act, NULL);
 130
 131         if (!nthreads)
 132                 nthreads = ncpus;
 133
 134         worker = calloc(nthreads, sizeof(*worker));
 135         if (!worker)
 136                 err(EXIT_FAILURE, "calloc");
 137
 138         printf("Run summary [PID %d]: Requeuing %d threads (from %p to %p), "
 139                "%d at a time.\n\n",
 140                getpid(), nthreads, &futex1, &futex2, nrequeue);
 141
 142         init_stats(&requeued_stats);
 143         init_stats(&requeuetime_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 < repeat && !done; j++) {
 150                 unsigned int nrequeued = 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 requeueing */
 166                 gettimeofday(&start, NULL);
 167                 for (nrequeued = 0; nrequeued < nthreads; nrequeued += nrequeue)
 168                         /*
 169                          * Do not wakeup any tasks blocked on futex1, allowing
 170                          * us to really measure futex_wait functionality.
 171                          */
 172                         futex_cmp_requeue(&futex1, 0, &futex2, 0, nrequeue,
 173                                           FUTEX_PRIVATE_FLAG);
 174                 gettimeofday(&end, NULL);
 175                 timersub(&end, &start, &runtime);
 176
 177                 update_stats(&requeued_stats, nrequeued);
 178                 update_stats(&requeuetime_stats, runtime.tv_usec);
 179
 180                 if (!silent) {
 181                         printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
 182                                j + 1, nrequeued, nthreads, runtime.tv_usec/1e3);
 183                 }
 184
 185                 /* everybody should be blocked on futex2, wake'em up */
 186                 nrequeued = futex_wake(&futex2, nthreads, FUTEX_PRIVATE_FLAG);
 187                 if (nthreads != nrequeued)
 188                         warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
 189
 190                 for (i = 0; i < nthreads; i++) {
 191                         ret = pthread_join(worker[i], NULL);
 192                         if (ret)
 193                                 err(EXIT_FAILURE, "pthread_join");
 194                 }
 195
 196         }
 197
 198         /* cleanup & report results */
 199         pthread_cond_destroy(&thread_parent);
 200         pthread_cond_destroy(&thread_worker);
 201         pthread_mutex_destroy(&thread_lock);
 202         pthread_attr_destroy(&thread_attr);
 203
 204         print_summary();
 205
 206         free(worker);
 207         return ret;
 208 err:
 209         usage_with_options(bench_futex_requeue_usage, options);
 210         exit(EXIT_FAILURE);
 211 }