1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com> 4 * 5 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time. 6 * 7 * This program is particularly useful to measure the latency of nthread wakeups 8 * in non-error situations: all waiters are queued and all wake calls wakeup 9 * one or more tasks, and thus the waitqueue is never empty. 10 */ 11 12 /* For the CLR_() macros */ 13 #include <string.h> 14 #include <pthread.h> 15 16 #include <signal.h> 17 #include "../util/stat.h" 18 #include <subcmd/parse-options.h> 19 #include <linux/compiler.h> 20 #include <linux/kernel.h> 21 #include <linux/time64.h> 22 #include <errno.h> 23 #include <perf/cpumap.h> 24 #include "bench.h" 25 #include "futex.h" 26 27 #include <err.h> 28 #include <stdlib.h> 29 #include <sys/time.h> 30 31 /* all threads will block on the same futex */ 32 static u_int32_t futex1 = 0; 33 34 /* 35 * How many wakeups to do at a time. 36 * Default to 1 in order to make the kernel work more. 37 */ 38 static unsigned int nwakes = 1; 39 40 pthread_t *worker; 41 static bool done = false, silent = false, fshared = false; 42 static pthread_mutex_t thread_lock; 43 static pthread_cond_t thread_parent, thread_worker; 44 static struct stats waketime_stats, wakeup_stats; 45 static unsigned int threads_starting, nthreads = 0; 46 static int futex_flag = 0; 47 48 static const struct option options[] = { 49 OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"), 50 OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"), 51 OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"), 52 OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"), 53 OPT_END() 54 }; 55 56 static const char * const bench_futex_wake_usage[] = { 57 "perf bench futex wake <options>", 58 NULL 59 }; 60 61 static void *workerfn(void *arg __maybe_unused) 62 { 63 pthread_mutex_lock(&thread_lock); 64 threads_starting--; 65 if (!threads_starting) 66 pthread_cond_signal(&thread_parent); 67 pthread_cond_wait(&thread_worker, &thread_lock); 68 pthread_mutex_unlock(&thread_lock); 69 70 while (1) { 71 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR) 72 break; 73 } 74 75 pthread_exit(NULL); 76 return NULL; 77 } 78 79 static void print_summary(void) 80 { 81 double waketime_avg = avg_stats(&waketime_stats); 82 double waketime_stddev = stddev_stats(&waketime_stats); 83 unsigned int wakeup_avg = avg_stats(&wakeup_stats); 84 85 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n", 86 wakeup_avg, 87 nthreads, 88 waketime_avg / USEC_PER_MSEC, 89 rel_stddev_stats(waketime_stddev, waketime_avg)); 90 } 91 92 static void block_threads(pthread_t *w, 93 pthread_attr_t thread_attr, struct perf_cpu_map *cpu) 94 { 95 cpu_set_t cpuset; 96 unsigned int i; 97 98 threads_starting = nthreads; 99 100 /* create and block all threads */ 101 for (i = 0; i < nthreads; i++) { 102 CPU_ZERO(&cpuset); 103 CPU_SET(cpu->map[i % cpu->nr], &cpuset); 104 105 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset)) 106 err(EXIT_FAILURE, "pthread_attr_setaffinity_np"); 107 108 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) 109 err(EXIT_FAILURE, "pthread_create"); 110 } 111 } 112 113 static void toggle_done(int sig __maybe_unused, 114 siginfo_t *info __maybe_unused, 115 void *uc __maybe_unused) 116 { 117 done = true; 118 } 119 120 int bench_futex_wake(int argc, const char **argv) 121 { 122 int ret = 0; 123 unsigned int i, j; 124 struct sigaction act; 125 pthread_attr_t thread_attr; 126 struct perf_cpu_map *cpu; 127 128 argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0); 129 if (argc) { 130 usage_with_options(bench_futex_wake_usage, options); 131 exit(EXIT_FAILURE); 132 } 133 134 cpu = perf_cpu_map__new(NULL); 135 if (!cpu) 136 err(EXIT_FAILURE, "calloc"); 137 138 memset(&act, 0, sizeof(act)); 139 sigfillset(&act.sa_mask); 140 act.sa_sigaction = toggle_done; 141 sigaction(SIGINT, &act, NULL); 142 143 if (!nthreads) 144 nthreads = cpu->nr; 145 146 worker = calloc(nthreads, sizeof(*worker)); 147 if (!worker) 148 err(EXIT_FAILURE, "calloc"); 149 150 if (!fshared) 151 futex_flag = FUTEX_PRIVATE_FLAG; 152 153 printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), " 154 "waking up %d at a time.\n\n", 155 getpid(), nthreads, fshared ? "shared":"private", &futex1, nwakes); 156 157 init_stats(&wakeup_stats); 158 init_stats(&waketime_stats); 159 pthread_attr_init(&thread_attr); 160 pthread_mutex_init(&thread_lock, NULL); 161 pthread_cond_init(&thread_parent, NULL); 162 pthread_cond_init(&thread_worker, NULL); 163 164 for (j = 0; j < bench_repeat && !done; j++) { 165 unsigned int nwoken = 0; 166 struct timeval start, end, runtime; 167 168 /* create, launch & block all threads */ 169 block_threads(worker, thread_attr, cpu); 170 171 /* make sure all threads are already blocked */ 172 pthread_mutex_lock(&thread_lock); 173 while (threads_starting) 174 pthread_cond_wait(&thread_parent, &thread_lock); 175 pthread_cond_broadcast(&thread_worker); 176 pthread_mutex_unlock(&thread_lock); 177 178 usleep(100000); 179 180 /* Ok, all threads are patiently blocked, start waking folks up */ 181 gettimeofday(&start, NULL); 182 while (nwoken != nthreads) 183 nwoken += futex_wake(&futex1, nwakes, futex_flag); 184 gettimeofday(&end, NULL); 185 timersub(&end, &start, &runtime); 186 187 update_stats(&wakeup_stats, nwoken); 188 update_stats(&waketime_stats, runtime.tv_usec); 189 190 if (!silent) { 191 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n", 192 j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC); 193 } 194 195 for (i = 0; i < nthreads; i++) { 196 ret = pthread_join(worker[i], NULL); 197 if (ret) 198 err(EXIT_FAILURE, "pthread_join"); 199 } 200 201 } 202 203 /* cleanup & report results */ 204 pthread_cond_destroy(&thread_parent); 205 pthread_cond_destroy(&thread_worker); 206 pthread_mutex_destroy(&thread_lock); 207 pthread_attr_destroy(&thread_attr); 208 209 print_summary(); 210 211 free(worker); 212 return ret; 213 } 214