linux/tools/perf/bench/futex-requeue.c
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   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 <perf/cpumap.h>
  24#include "bench.h"
  25#include "futex.h"
  26
  27#include <err.h>
  28#include <stdlib.h>
  29#include <sys/time.h>
  30
  31static u_int32_t futex1 = 0, futex2 = 0;
  32
  33/*
  34 * How many tasks to requeue at a time.
  35 * Default to 1 in order to make the kernel work more.
  36 */
  37static unsigned int nrequeue = 1;
  38
  39static pthread_t *worker;
  40static bool done = false, silent = false, fshared = false;
  41static pthread_mutex_t thread_lock;
  42static pthread_cond_t thread_parent, thread_worker;
  43static struct stats requeuetime_stats, requeued_stats;
  44static unsigned int threads_starting, nthreads = 0;
  45static int futex_flag = 0;
  46
  47static const struct option options[] = {
  48        OPT_UINTEGER('t', "threads",  &nthreads, "Specify amount of threads"),
  49        OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue at once"),
  50        OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
  51        OPT_BOOLEAN( 'S', "shared",   &fshared,  "Use shared futexes instead of private ones"),
  52        OPT_END()
  53};
  54
  55static const char * const bench_futex_requeue_usage[] = {
  56        "perf bench futex requeue <options>",
  57        NULL
  58};
  59
  60static void print_summary(void)
  61{
  62        double requeuetime_avg = avg_stats(&requeuetime_stats);
  63        double requeuetime_stddev = stddev_stats(&requeuetime_stats);
  64        unsigned int requeued_avg = avg_stats(&requeued_stats);
  65
  66        printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
  67               requeued_avg,
  68               nthreads,
  69               requeuetime_avg / USEC_PER_MSEC,
  70               rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
  71}
  72
  73static void *workerfn(void *arg __maybe_unused)
  74{
  75        pthread_mutex_lock(&thread_lock);
  76        threads_starting--;
  77        if (!threads_starting)
  78                pthread_cond_signal(&thread_parent);
  79        pthread_cond_wait(&thread_worker, &thread_lock);
  80        pthread_mutex_unlock(&thread_lock);
  81
  82        futex_wait(&futex1, 0, NULL, futex_flag);
  83        return NULL;
  84}
  85
  86static void block_threads(pthread_t *w,
  87                          pthread_attr_t thread_attr, struct perf_cpu_map *cpu)
  88{
  89        cpu_set_t cpuset;
  90        unsigned int i;
  91
  92        threads_starting = nthreads;
  93
  94        /* create and block all threads */
  95        for (i = 0; i < nthreads; i++) {
  96                CPU_ZERO(&cpuset);
  97                CPU_SET(cpu->map[i % cpu->nr], &cpuset);
  98
  99                if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
 100                        err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 101
 102                if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
 103                        err(EXIT_FAILURE, "pthread_create");
 104        }
 105}
 106
 107static void toggle_done(int sig __maybe_unused,
 108                        siginfo_t *info __maybe_unused,
 109                        void *uc __maybe_unused)
 110{
 111        done = true;
 112}
 113
 114int bench_futex_requeue(int argc, const char **argv)
 115{
 116        int ret = 0;
 117        unsigned int i, j;
 118        struct sigaction act;
 119        pthread_attr_t thread_attr;
 120        struct perf_cpu_map *cpu;
 121
 122        argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
 123        if (argc)
 124                goto err;
 125
 126        cpu = perf_cpu_map__new(NULL);
 127        if (!cpu)
 128                err(EXIT_FAILURE, "cpu_map__new");
 129
 130        memset(&act, 0, sizeof(act));
 131        sigfillset(&act.sa_mask);
 132        act.sa_sigaction = toggle_done;
 133        sigaction(SIGINT, &act, NULL);
 134
 135        if (!nthreads)
 136                nthreads = cpu->nr;
 137
 138        worker = calloc(nthreads, sizeof(*worker));
 139        if (!worker)
 140                err(EXIT_FAILURE, "calloc");
 141
 142        if (!fshared)
 143                futex_flag = FUTEX_PRIVATE_FLAG;
 144
 145        if (nrequeue > nthreads)
 146                nrequeue = nthreads;
 147
 148        printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
 149               "%d at a time.\n\n",  getpid(), nthreads,
 150               fshared ? "shared":"private", &futex1, &futex2, nrequeue);
 151
 152        init_stats(&requeued_stats);
 153        init_stats(&requeuetime_stats);
 154        pthread_attr_init(&thread_attr);
 155        pthread_mutex_init(&thread_lock, NULL);
 156        pthread_cond_init(&thread_parent, NULL);
 157        pthread_cond_init(&thread_worker, NULL);
 158
 159        for (j = 0; j < bench_repeat && !done; j++) {
 160                unsigned int nrequeued = 0;
 161                struct timeval start, end, runtime;
 162
 163                /* create, launch & block all threads */
 164                block_threads(worker, thread_attr, cpu);
 165
 166                /* make sure all threads are already blocked */
 167                pthread_mutex_lock(&thread_lock);
 168                while (threads_starting)
 169                        pthread_cond_wait(&thread_parent, &thread_lock);
 170                pthread_cond_broadcast(&thread_worker);
 171                pthread_mutex_unlock(&thread_lock);
 172
 173                usleep(100000);
 174
 175                /* Ok, all threads are patiently blocked, start requeueing */
 176                gettimeofday(&start, NULL);
 177                while (nrequeued < nthreads) {
 178                        /*
 179                         * Do not wakeup any tasks blocked on futex1, allowing
 180                         * us to really measure futex_wait functionality.
 181                         */
 182                        nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
 183                                                       nrequeue, futex_flag);
 184                }
 185
 186                gettimeofday(&end, NULL);
 187                timersub(&end, &start, &runtime);
 188
 189                update_stats(&requeued_stats, nrequeued);
 190                update_stats(&requeuetime_stats, runtime.tv_usec);
 191
 192                if (!silent) {
 193                        printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
 194                               j + 1, nrequeued, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
 195                }
 196
 197                /* everybody should be blocked on futex2, wake'em up */
 198                nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
 199                if (nthreads != nrequeued)
 200                        warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
 201
 202                for (i = 0; i < nthreads; i++) {
 203                        ret = pthread_join(worker[i], NULL);
 204                        if (ret)
 205                                err(EXIT_FAILURE, "pthread_join");
 206                }
 207        }
 208
 209        /* cleanup & report results */
 210        pthread_cond_destroy(&thread_parent);
 211        pthread_cond_destroy(&thread_worker);
 212        pthread_mutex_destroy(&thread_lock);
 213        pthread_attr_destroy(&thread_attr);
 214
 215        print_summary();
 216
 217        free(worker);
 218        return ret;
 219err:
 220        usage_with_options(bench_futex_requeue_usage, options);
 221        exit(EXIT_FAILURE);
 222}
 223
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