// SPDX-License-Identifier: GPL-2.0 /* * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com> * * 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 <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 <perf/cpumap.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 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"), OPT_END() }; static const char * const bench_futex_wake_usage[] = { "perf bench futex wake <options>", NULL }; 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; } 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)); } static void block_threads(pthread_t *w, pthread_attr_t thread_attr, struct perf_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_wake(int argc, const char **argv) { int ret = 0; unsigned int i, j; struct sigaction act; pthread_attr_t thread_attr; struct perf_cpu_map *cpu; argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0); if (argc) { usage_with_options(bench_futex_wake_usage, options); exit(EXIT_FAILURE); } cpu = perf_cpu_map__new(NULL); if (!cpu) err(EXIT_FAILURE, "calloc"); memset(&act, 0, sizeof(act)); 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; 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, 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 */ 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; }