cregit-Linux how code gets into the kernel

Release 4.10 tools/perf/bench/futex-requeue.c

Directory: tools/perf/bench
 * Copyright (C) 2013  Davidlohr Bueso <>
 * 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 <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 <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 ncpus, 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"),

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

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)); }


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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; }


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static void block_threads(pthread_t *w, pthread_attr_t thread_attr) { cpu_set_t cpu; unsigned int i; threads_starting = nthreads; /* create and block all threads */ for (i = 0; i < nthreads; i++) { CPU_ZERO(&cpu); CPU_SET(i % ncpus, &cpu); if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu)) err(EXIT_FAILURE, "pthread_attr_setaffinity_np"); if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) err(EXIT_FAILURE, "pthread_create"); } }


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


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int bench_futex_requeue(int argc, const char **argv, const char *prefix __maybe_unused) { int ret = 0; unsigned int i, j; struct sigaction act; pthread_attr_t thread_attr; argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0); if (argc) goto err; ncpus = sysconf(_SC_NPROCESSORS_ONLN); sigfillset(&act.sa_mask); act.sa_sigaction = toggle_done; sigaction(SIGINT, &act, NULL); if (!nthreads) nthreads = ncpus; else nthreads = futexbench_sanitize_numeric(nthreads); 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); /* 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); }


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Directory: tools/perf/bench
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