linux/tools/perf/bench/futex-wake.c
<<
>>
Prefs
   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 <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
  31/* all threads will block on the same futex */
  32static 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 */
  38static unsigned int nwakes = 1;
  39
  40pthread_t *worker;
  41static bool done = false, silent = false, fshared = false;
  42static pthread_mutex_t thread_lock;
  43static pthread_cond_t thread_parent, thread_worker;
  44static struct stats waketime_stats, wakeup_stats;
  45static unsigned int threads_starting, nthreads = 0;
  46static int futex_flag = 0;
  47
  48static 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
  56static const char * const bench_futex_wake_usage[] = {
  57        "perf bench futex wake <options>",
  58        NULL
  59};
  60
  61static 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
  79static 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
  92static void block_threads(pthread_t *w,
  93                          pthread_attr_t thread_attr, struct perf_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
 113static void toggle_done(int sig __maybe_unused,
 114                        siginfo_t *info __maybe_unused,
 115                        void *uc __maybe_unused)
 116{
 117        done = true;
 118}
 119
 120int 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 perf_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 = perf_cpu_map__new(NULL);
 135        if (!cpu)
 136                err(EXIT_FAILURE, "calloc");
 137
 138        memset(&act, 0, sizeof(act));
 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}
 214
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.