cregit-Linux how code gets into the kernel

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

Directory: tools/perf/bench
 * Copyright (C) 2013  Davidlohr Bueso <>
 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
 * This program is particularly useful to measure the latency of nthread wakeups
 * in non-error situations:  all waiters are queued and all wake calls wakeup
 * one or more tasks, and thus the waitqueue is never empty.

/* 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>

/* all threads will block on the same futex */

static u_int32_t futex1 = 0;

 * How many wakeups to do at a time.
 * Default to 1 in order to make the kernel work more.

static unsigned int nwakes = 1;

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 waketime_stats, wakeup_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('w', "nwakes",  &nwakes,   "Specify amount of threads to wake 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_wake_usage[] = {
	"perf bench futex wake <options>",

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); while (1) { if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR) break; } pthread_exit(NULL); return NULL; }


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static void print_summary(void) { double waketime_avg = avg_stats(&waketime_stats); double waketime_stddev = stddev_stats(&waketime_stats); unsigned int wakeup_avg = avg_stats(&wakeup_stats); printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n", wakeup_avg, nthreads, waketime_avg / USEC_PER_MSEC, rel_stddev_stats(waketime_stddev, waketime_avg)); }


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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_wake(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_wake_usage, 0); if (argc) { usage_with_options(bench_futex_wake_usage, options); exit(EXIT_FAILURE); } ncpus = sysconf(_SC_NPROCESSORS_ONLN); nwakes = futexbench_sanitize_numeric(nwakes); 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; printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), " "waking up %d at a time.\n\n", getpid(), nthreads, fshared ? "shared":"private", &futex1, 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++) { unsigned int nwoken = 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 waking folks up */ gettimeofday(&start, NULL); while (nwoken != nthreads) nwoken += futex_wake(&futex1, nwakes, futex_flag); gettimeofday(&end, NULL); timersub(&end, &start, &runtime); update_stats(&wakeup_stats, nwoken); update_stats(&waketime_stats, runtime.tv_usec); if (!silent) { printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n", j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC); } 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; }


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Directory: tools/perf/bench
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