futex-wake-parallel.c

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// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Davidlohr Bueso.
 *
 * Block a bunch of threads and let parallel waker threads wakeup an
 * equal amount of them. The program output reflects the avg latency
 * for each individual thread to service its share of work. Ultimately
 * it can be used to measure futex_wake() changes.
 */
#include "bench.h"
#include <linux/compiler.h>
#include "../util/debug.h"

#ifndef HAVE_PTHREAD_BARRIER
int bench_futex_wake_parallel(int argc __maybe_unused, const char **argv __maybe_unused)
{
    pr_err("%s: pthread_barrier_t unavailable, disabling this test...\n", __func__);
    return 0;
}
#else /* HAVE_PTHREAD_BARRIER */
/* For the CLR_() macros */
#include <string.h>
#include <pthread.h>

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

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

struct thread_data {
    pthread_t worker;
    unsigned int nwoken;
    struct timeval runtime;
};

static unsigned int nwakes = 1;

/* all threads will block on the same futex -- hash bucket chaos ;) */
static u_int32_t futex = 0;

static pthread_t *blocked_worker;
static bool done = false, silent = false, fshared = false;
static unsigned int nblocked_threads = 0, nwaking_threads = 0;
static pthread_mutex_t thread_lock;
static pthread_cond_t thread_parent, thread_worker;
static pthread_barrier_t barrier;
static struct stats waketime_stats, wakeup_stats;
static unsigned int threads_starting;
static int futex_flag = 0;

static const struct option options[] = {
    OPT_UINTEGER('t', "threads", &nblocked_threads, "Specify amount of threads"),
    OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
    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_wake_parallel_usage[] = {
    "perf bench futex wake-parallel <options>",
    NULL
};

static void *waking_workerfn(void *arg)
{
    struct thread_data *waker = (struct thread_data *) arg;
    struct timeval start, end;

    pthread_barrier_wait(&barrier);

    gettimeofday(&start, NULL);

    waker->nwoken = futex_wake(&futex, nwakes, futex_flag);
    if (waker->nwoken != nwakes)
        warnx("couldn't wakeup all tasks (%d/%d)",
              waker->nwoken, nwakes);

    gettimeofday(&end, NULL);
    timersub(&end, &start, &waker->runtime);

    pthread_exit(NULL);
    return NULL;
}

static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
{
    unsigned int i;

    pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE);

    pthread_barrier_init(&barrier, NULL, nwaking_threads + 1);

    /* create and block all threads */
    for (i = 0; i < nwaking_threads; i++) {
        /*
         * Thread creation order will impact per-thread latency
         * as it will affect the order to acquire the hb spinlock.
         * For now let the scheduler decide.
         */
        if (pthread_create(&td[i].worker, &thread_attr,
                   waking_workerfn, (void *)&td[i]))
            err(EXIT_FAILURE, "pthread_create");
    }

    pthread_barrier_wait(&barrier);

    for (i = 0; i < nwaking_threads; i++)
        if (pthread_join(td[i].worker, NULL))
            err(EXIT_FAILURE, "pthread_join");

    pthread_barrier_destroy(&barrier);
}

static void *blocked_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);

    while (1) { /* handle spurious wakeups */
        if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
            break;
    }

    pthread_exit(NULL);
    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 = nblocked_threads;

    /* create and block all threads */
    for (i = 0; i < nblocked_threads; 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, blocked_workerfn, NULL))
            err(EXIT_FAILURE, "pthread_create");
    }
}

static void print_run(struct thread_data *waking_worker, unsigned int run_num)
{
    unsigned int i, wakeup_avg;
    double waketime_avg, waketime_stddev;
    struct stats __waketime_stats, __wakeup_stats;

    init_stats(&__wakeup_stats);
    init_stats(&__waketime_stats);

    for (i = 0; i < nwaking_threads; i++) {
        update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
        update_stats(&__wakeup_stats, waking_worker[i].nwoken);
    }

    waketime_avg = avg_stats(&__waketime_stats);
    waketime_stddev = stddev_stats(&__waketime_stats);
    wakeup_avg = avg_stats(&__wakeup_stats);

    printf("[Run %d]: Avg per-thread latency (waking %d/%d threads) "
           "in %.4f ms (+-%.2f%%)\n", run_num + 1, wakeup_avg,
           nblocked_threads, waketime_avg / USEC_PER_MSEC,
           rel_stddev_stats(waketime_stddev, waketime_avg));
}

static void print_summary(void)
{
    unsigned int wakeup_avg;
    double waketime_avg, waketime_stddev;

    waketime_avg = avg_stats(&waketime_stats);
    waketime_stddev = stddev_stats(&waketime_stats);
    wakeup_avg = avg_stats(&wakeup_stats);

    printf("Avg per-thread latency (waking %d/%d threads) in %.4f ms (+-%.2f%%)\n",
           wakeup_avg,
           nblocked_threads,
           waketime_avg / USEC_PER_MSEC,
           rel_stddev_stats(waketime_stddev, waketime_avg));
}


static void do_run_stats(struct thread_data *waking_worker)
{
    unsigned int i;

    for (i = 0; i < nwaking_threads; i++) {
        update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
        update_stats(&wakeup_stats, waking_worker[i].nwoken);
    }

}

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

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

    argc = parse_options(argc, argv, options,
                 bench_futex_wake_parallel_usage, 0);
    if (argc) {
        usage_with_options(bench_futex_wake_parallel_usage, options);
        exit(EXIT_FAILURE);
    }

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

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

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

    /* some sanity checks */
    if (nwaking_threads > nblocked_threads || !nwaking_threads)
        nwaking_threads = nblocked_threads;

    if (nblocked_threads % nwaking_threads)
        errx(EXIT_FAILURE, "Must be perfectly divisible");
    /*
     * Each thread will wakeup nwakes tasks in
     * a single futex_wait call.
     */
    nwakes = nblocked_threads/nwaking_threads;

    blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
    if (!blocked_worker)
        err(EXIT_FAILURE, "calloc");

    if (!fshared)
        futex_flag = FUTEX_PRIVATE_FLAG;

    printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
           "futex %p), %d threads waking up %d at a time.\n\n",
           getpid(), nblocked_threads, fshared ? "shared":"private",
           &futex, nwaking_threads, nwakes);

    init_stats(&wakeup_stats);
    init_stats(&waketime_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++) {
        waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
        if (!waking_worker)
            err(EXIT_FAILURE, "calloc");

        /* create, launch & block all threads */
        block_threads(blocked_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 waking folks up */
        wakeup_threads(waking_worker, thread_attr);

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

        do_run_stats(waking_worker);
        if (!silent)
            print_run(waking_worker, j);

        free(waking_worker);
    }

    /* 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(blocked_worker);
    return ret;
}
#endif /* HAVE_PTHREAD_BARRIER */