1 /* 2 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com> 3 * 4 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time. 5 * 6 * This program is particularly useful to measure the latency of nthread wakeups 7 * in non-error situations: all waiters are queued and all wake calls wakeup 8 * one or more tasks, and thus the waitqueue is never empty. 9 */ 10 11 #include "../perf.h" 12 #include "../util/util.h" 13 #include "../util/stat.h" 14 #include "../util/parse-options.h" 15 #include "../util/header.h" 16 #include "bench.h" 17 #include "futex.h" 18 19 #include <err.h> 20 #include <stdlib.h> 21 #include <sys/time.h> 22 #include <pthread.h> 23 24 /* all threads will block on the same futex */ 25 static u_int32_t futex1 = 0; 26 27 /* 28 * How many wakeups to do at a time. 29 * Default to 1 in order to make the kernel work more. 30 */ 31 static unsigned int nwakes = 1; 32 33 /* 34 * There can be significant variance from run to run, 35 * the more repeats, the more exact the overall avg and 36 * the better idea of the futex latency. 37 */ 38 static unsigned int repeat = 10; 39 40 pthread_t *worker; 41 static bool done = 0, silent = 0; 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 ncpus, threads_starting, nthreads = 0; 46 47 static const struct option options[] = { 48 OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"), 49 OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"), 50 OPT_UINTEGER('r', "repeat", &repeat, "Specify amount of times to repeat the run"), 51 OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"), 52 OPT_END() 53 }; 54 55 static const char * const bench_futex_wake_usage[] = { 56 "perf bench futex wake <options>", 57 NULL 58 }; 59 60 static void *workerfn(void *arg __maybe_unused) 61 { 62 pthread_mutex_lock(&thread_lock); 63 threads_starting--; 64 if (!threads_starting) 65 pthread_cond_signal(&thread_parent); 66 pthread_cond_wait(&thread_worker, &thread_lock); 67 pthread_mutex_unlock(&thread_lock); 68 69 futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG); 70 return NULL; 71 } 72 73 static void print_summary(void) 74 { 75 double waketime_avg = avg_stats(&waketime_stats); 76 double waketime_stddev = stddev_stats(&waketime_stats); 77 unsigned int wakeup_avg = avg_stats(&wakeup_stats); 78 79 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n", 80 wakeup_avg, 81 nthreads, 82 waketime_avg/1e3, 83 rel_stddev_stats(waketime_stddev, waketime_avg)); 84 } 85 86 static void block_threads(pthread_t *w, 87 pthread_attr_t thread_attr) 88 { 89 cpu_set_t cpu; 90 unsigned int i; 91 92 threads_starting = nthreads; 93 94 /* create and block all threads */ 95 for (i = 0; i < nthreads; i++) { 96 CPU_ZERO(&cpu); 97 CPU_SET(i % ncpus, &cpu); 98 99 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu)) 100 err(EXIT_FAILURE, "pthread_attr_setaffinity_np"); 101 102 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) 103 err(EXIT_FAILURE, "pthread_create"); 104 } 105 } 106 107 static void toggle_done(int sig __maybe_unused, 108 siginfo_t *info __maybe_unused, 109 void *uc __maybe_unused) 110 { 111 done = true; 112 } 113 114 int bench_futex_wake(int argc, const char **argv, 115 const char *prefix __maybe_unused) 116 { 117 int ret = 0; 118 unsigned int i, j; 119 struct sigaction act; 120 pthread_attr_t thread_attr; 121 122 argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0); 123 if (argc) { 124 usage_with_options(bench_futex_wake_usage, options); 125 exit(EXIT_FAILURE); 126 } 127 128 ncpus = sysconf(_SC_NPROCESSORS_ONLN); 129 130 sigfillset(&act.sa_mask); 131 act.sa_sigaction = toggle_done; 132 sigaction(SIGINT, &act, NULL); 133 134 if (!nthreads) 135 nthreads = ncpus; 136 137 worker = calloc(nthreads, sizeof(*worker)); 138 if (!worker) 139 err(EXIT_FAILURE, "calloc"); 140 141 printf("Run summary [PID %d]: blocking on %d threads (at futex %p), " 142 "waking up %d at a time.\n\n", 143 getpid(), nthreads, &futex1, nwakes); 144 145 init_stats(&wakeup_stats); 146 init_stats(&waketime_stats); 147 pthread_attr_init(&thread_attr); 148 pthread_mutex_init(&thread_lock, NULL); 149 pthread_cond_init(&thread_parent, NULL); 150 pthread_cond_init(&thread_worker, NULL); 151 152 for (j = 0; j < repeat && !done; j++) { 153 unsigned int nwoken = 0; 154 struct timeval start, end, runtime; 155 156 /* create, launch & block all threads */ 157 block_threads(worker, thread_attr); 158 159 /* make sure all threads are already blocked */ 160 pthread_mutex_lock(&thread_lock); 161 while (threads_starting) 162 pthread_cond_wait(&thread_parent, &thread_lock); 163 pthread_cond_broadcast(&thread_worker); 164 pthread_mutex_unlock(&thread_lock); 165 166 usleep(100000); 167 168 /* Ok, all threads are patiently blocked, start waking folks up */ 169 gettimeofday(&start, NULL); 170 while (nwoken != nthreads) 171 nwoken += futex_wake(&futex1, nwakes, FUTEX_PRIVATE_FLAG); 172 gettimeofday(&end, NULL); 173 timersub(&end, &start, &runtime); 174 175 update_stats(&wakeup_stats, nwoken); 176 update_stats(&waketime_stats, runtime.tv_usec); 177 178 if (!silent) { 179 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n", 180 j + 1, nwoken, nthreads, runtime.tv_usec/1e3); 181 } 182 183 for (i = 0; i < nthreads; i++) { 184 ret = pthread_join(worker[i], NULL); 185 if (ret) 186 err(EXIT_FAILURE, "pthread_join"); 187 } 188 189 } 190 191 /* cleanup & report results */ 192 pthread_cond_destroy(&thread_parent); 193 pthread_cond_destroy(&thread_worker); 194 pthread_mutex_destroy(&thread_lock); 195 pthread_attr_destroy(&thread_attr); 196 197 print_summary(); 198 199 free(worker); 200 return ret; 201 } 202