futex-requeue.c

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// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
 *
 * futex-requeue: Block a bunch of threads on futex1 and requeue them
 *                on futex2, N at a time.
 *
 * This program is particularly useful to measure the latency of nthread
 * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
 */

/* For the CLR_() macros */
#include <string.h>
#include <pthread.h>

#include <signal.h>
#include "../util/stat.h"
#include <subcmd/parse-options.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/time64.h>
#include <errno.h>
#include "bench.h"
#include "futex.h"
#include "cpumap.h"

#include <err.h>
#include <stdlib.h>
#include <sys/time.h>

static u_int32_t futex1 = 0, futex2 = 0;

/*
 * How many tasks to requeue at a time.
 * Default to 1 in order to make the kernel work more.
 */
static unsigned int nrequeue = 1;

static pthread_t *worker;
static bool done = false, silent = false, fshared = false;
static pthread_mutex_t thread_lock;
static pthread_cond_t thread_parent, thread_worker;
static struct stats requeuetime_stats, requeued_stats;
static unsigned int threads_starting, nthreads = 0;
static int futex_flag = 0;

static const struct option options[] = {
    OPT_UINTEGER('t', "threads",  &nthreads, "Specify amount of threads"),
    OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue at once"),
    OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
    OPT_BOOLEAN( 'S', "shared",   &fshared,  "Use shared futexes instead of private ones"),
    OPT_END()
};

static const char * const bench_futex_requeue_usage[] = {
    "perf bench futex requeue <options>",
    NULL
};

static void print_summary(void)
{
    double requeuetime_avg = avg_stats(&requeuetime_stats);
    double requeuetime_stddev = stddev_stats(&requeuetime_stats);
    unsigned int requeued_avg = avg_stats(&requeued_stats);

    printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
           requeued_avg,
           nthreads,
           requeuetime_avg / USEC_PER_MSEC,
           rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
}

static void *workerfn(void *arg __maybe_unused)
{
    pthread_mutex_lock(&thread_lock);
    threads_starting--;
    if (!threads_starting)
        pthread_cond_signal(&thread_parent);
    pthread_cond_wait(&thread_worker, &thread_lock);
    pthread_mutex_unlock(&thread_lock);

    futex_wait(&futex1, 0, NULL, futex_flag);
    return NULL;
}

static void block_threads(pthread_t *w,
              pthread_attr_t thread_attr, struct cpu_map *cpu)
{
    cpu_set_t cpuset;
    unsigned int i;

    threads_starting = nthreads;

    /* create and block all threads */
    for (i = 0; i < nthreads; i++) {
        CPU_ZERO(&cpuset);
        CPU_SET(cpu->map[i % cpu->nr], &cpuset);

        if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
            err(EXIT_FAILURE, "pthread_attr_setaffinity_np");

        if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
            err(EXIT_FAILURE, "pthread_create");
    }
}

static void toggle_done(int sig __maybe_unused,
            siginfo_t *info __maybe_unused,
            void *uc __maybe_unused)
{
    done = true;
}

int bench_futex_requeue(int argc, const char **argv)
{
    int ret = 0;
    unsigned int i, j;
    struct sigaction act;
    pthread_attr_t thread_attr;
    struct cpu_map *cpu;

    argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
    if (argc)
        goto err;

    cpu = cpu_map__new(NULL);
    if (!cpu)
        err(EXIT_FAILURE, "cpu_map__new");

    sigfillset(&act.sa_mask);
    act.sa_sigaction = toggle_done;
    sigaction(SIGINT, &act, NULL);

    if (!nthreads)
        nthreads = cpu->nr;

    worker = calloc(nthreads, sizeof(*worker));
    if (!worker)
        err(EXIT_FAILURE, "calloc");

    if (!fshared)
        futex_flag = FUTEX_PRIVATE_FLAG;

    if (nrequeue > nthreads)
        nrequeue = nthreads;

    printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
           "%d at a time.\n\n",  getpid(), nthreads,
           fshared ? "shared":"private", &futex1, &futex2, nrequeue);

    init_stats(&requeued_stats);
    init_stats(&requeuetime_stats);
    pthread_attr_init(&thread_attr);
    pthread_mutex_init(&thread_lock, NULL);
    pthread_cond_init(&thread_parent, NULL);
    pthread_cond_init(&thread_worker, NULL);

    for (j = 0; j < bench_repeat && !done; j++) {
        unsigned int nrequeued = 0;
        struct timeval start, end, runtime;

        /* create, launch & block all threads */
        block_threads(worker, thread_attr, cpu);

        /* make sure all threads are already blocked */
        pthread_mutex_lock(&thread_lock);
        while (threads_starting)
            pthread_cond_wait(&thread_parent, &thread_lock);
        pthread_cond_broadcast(&thread_worker);
        pthread_mutex_unlock(&thread_lock);

        usleep(100000);

        /* Ok, all threads are patiently blocked, start requeueing */
        gettimeofday(&start, NULL);
        while (nrequeued < nthreads) {
            /*
             * Do not wakeup any tasks blocked on futex1, allowing
             * us to really measure futex_wait functionality.
             */
            nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
                               nrequeue, futex_flag);
        }

        gettimeofday(&end, NULL);
        timersub(&end, &start, &runtime);

        update_stats(&requeued_stats, nrequeued);
        update_stats(&requeuetime_stats, runtime.tv_usec);

        if (!silent) {
            printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
                   j + 1, nrequeued, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
        }

        /* everybody should be blocked on futex2, wake'em up */
        nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
        if (nthreads != nrequeued)
            warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);

        for (i = 0; i < nthreads; i++) {
            ret = pthread_join(worker[i], NULL);
            if (ret)
                err(EXIT_FAILURE, "pthread_join");
        }
    }

    /* cleanup & report results */
    pthread_cond_destroy(&thread_parent);
    pthread_cond_destroy(&thread_worker);
    pthread_mutex_destroy(&thread_lock);
    pthread_attr_destroy(&thread_attr);

    print_summary();

    free(worker);
    return ret;
err:
    usage_with_options(bench_futex_requeue_usage, options);
    exit(EXIT_FAILURE);
}