futex-hash.c

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// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
 *
 * futex-hash: Stress the hell out of the Linux kernel futex uaddr hashing.
 *
 * This program is particularly useful for measuring the kernel's futex hash
 * table/function implementation. In order for it to make sense, use with as
 * many threads and futexes as possible.
 */

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

#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <sys/time.h>

#include "../util/stat.h"
#include <subcmd/parse-options.h>
#include "bench.h"
#include "futex.h"
#include "cpumap.h"

#include <err.h>

static unsigned int nthreads = 0;
static unsigned int nsecs    = 10;
/* amount of futexes per thread */
static unsigned int nfutexes = 1024;
static bool fshared = false, done = false, silent = false;
static int futex_flag = 0;

struct timeval start, end, runtime;
static pthread_mutex_t thread_lock;
static unsigned int threads_starting;
static struct stats throughput_stats;
static pthread_cond_t thread_parent, thread_worker;

struct worker {
    int tid;
    u_int32_t *futex;
    pthread_t thread;
    unsigned long ops;
};

static const struct option options[] = {
    OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
    OPT_UINTEGER('r', "runtime", &nsecs,    "Specify runtime (in seconds)"),
    OPT_UINTEGER('f', "futexes", &nfutexes, "Specify amount of futexes per 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_hash_usage[] = {
    "perf bench futex hash <options>",
    NULL
};

static void *workerfn(void *arg)
{
    int ret;
    struct worker *w = (struct worker *) arg;
    unsigned int i;
    unsigned long ops = w->ops; /* avoid cacheline bouncing */

    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);

    do {
        for (i = 0; i < nfutexes; i++, ops++) {
            /*
             * We want the futex calls to fail in order to stress
             * the hashing of uaddr and not measure other steps,
             * such as internal waitqueue handling, thus enlarging
             * the critical region protected by hb->lock.
             */
            ret = futex_wait(&w->futex[i], 1234, NULL, futex_flag);
            if (!silent &&
                (!ret || errno != EAGAIN || errno != EWOULDBLOCK))
                warn("Non-expected futex return call");
        }
    }  while (!done);

    w->ops = ops;
    return NULL;
}

static void toggle_done(int sig __maybe_unused,
            siginfo_t *info __maybe_unused,
            void *uc __maybe_unused)
{
    /* inform all threads that we're done for the day */
    done = true;
    gettimeofday(&end, NULL);
    timersub(&end, &start, &runtime);
}

static void print_summary(void)
{
    unsigned long avg = avg_stats(&throughput_stats);
    double stddev = stddev_stats(&throughput_stats);

    printf("%sAveraged %ld operations/sec (+- %.2f%%), total secs = %d\n",
           !silent ? "\n" : "", avg, rel_stddev_stats(stddev, avg),
           (int) runtime.tv_sec);
}

int bench_futex_hash(int argc, const char **argv)
{
    int ret = 0;
    cpu_set_t cpuset;
    struct sigaction act;
    unsigned int i;
    pthread_attr_t thread_attr;
    struct worker *worker = NULL;
    struct cpu_map *cpu;

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

    cpu = cpu_map__new(NULL);
    if (!cpu)
        goto errmem;

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

    if (!nthreads) /* default to the number of CPUs */
        nthreads = cpu->nr;

    worker = calloc(nthreads, sizeof(*worker));
    if (!worker)
        goto errmem;

    if (!fshared)
        futex_flag = FUTEX_PRIVATE_FLAG;

    printf("Run summary [PID %d]: %d threads, each operating on %d [%s] futexes for %d secs.\n\n",
           getpid(), nthreads, nfutexes, fshared ? "shared":"private", nsecs);

    init_stats(&throughput_stats);
    pthread_mutex_init(&thread_lock, NULL);
    pthread_cond_init(&thread_parent, NULL);
    pthread_cond_init(&thread_worker, NULL);

    threads_starting = nthreads;
    pthread_attr_init(&thread_attr);
    gettimeofday(&start, NULL);
    for (i = 0; i < nthreads; i++) {
        worker[i].tid = i;
        worker[i].futex = calloc(nfutexes, sizeof(*worker[i].futex));
        if (!worker[i].futex)
            goto errmem;

        CPU_ZERO(&cpuset);
        CPU_SET(cpu->map[i % cpu->nr], &cpuset);

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

        ret = pthread_create(&worker[i].thread, &thread_attr, workerfn,
                     (void *)(struct worker *) &worker[i]);
        if (ret)
            err(EXIT_FAILURE, "pthread_create");

    }
    pthread_attr_destroy(&thread_attr);

    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);

    sleep(nsecs);
    toggle_done(0, NULL, NULL);

    for (i = 0; i < nthreads; i++) {
        ret = pthread_join(worker[i].thread, 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);

    for (i = 0; i < nthreads; i++) {
        unsigned long t = worker[i].ops/runtime.tv_sec;
        update_stats(&throughput_stats, t);
        if (!silent) {
            if (nfutexes == 1)
                printf("[thread %2d] futex: %p [ %ld ops/sec ]\n",
                       worker[i].tid, &worker[i].futex[0], t);
            else
                printf("[thread %2d] futexes: %p ... %p [ %ld ops/sec ]\n",
                       worker[i].tid, &worker[i].futex[0],
                       &worker[i].futex[nfutexes-1], t);
        }

        free(worker[i].futex);
    }

    print_summary();

    free(worker);
    free(cpu);
    return ret;
errmem:
    err(EXIT_FAILURE, "calloc");
}