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 pthread_t *worker; 34 static bool done = false, silent = false, fshared = false; 35 static pthread_mutex_t thread_lock; 36 static pthread_cond_t thread_parent, thread_worker; 37 static struct stats waketime_stats, wakeup_stats; 38 static unsigned int ncpus, threads_starting, nthreads = 0; 39 static int futex_flag = 0; 40 41 static const struct option options[] = { 42 OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"), 43 OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"), 44 OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"), 45 OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"), 46 OPT_END() 47 }; 48 49 static const char * const bench_futex_wake_usage[] = { 50 "perf bench futex wake <options>", 51 NULL 52 }; 53 54 static void *workerfn(void *arg __maybe_unused) 55 { 56 pthread_mutex_lock(&thread_lock); 57 threads_starting--; 58 if (!threads_starting) 59 pthread_cond_signal(&thread_parent); 60 pthread_cond_wait(&thread_worker, &thread_lock); 61 pthread_mutex_unlock(&thread_lock); 62 63 futex_wait(&futex1, 0, NULL, futex_flag); 64 return NULL; 65 } 66 67 static void print_summary(void) 68 { 69 double waketime_avg = avg_stats(&waketime_stats); 70 double waketime_stddev = stddev_stats(&waketime_stats); 71 unsigned int wakeup_avg = avg_stats(&wakeup_stats); 72 73 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n", 74 wakeup_avg, 75 nthreads, 76 waketime_avg/1e3, 77 rel_stddev_stats(waketime_stddev, waketime_avg)); 78 } 79 80 static void block_threads(pthread_t *w, 81 pthread_attr_t thread_attr) 82 { 83 cpu_set_t cpu; 84 unsigned int i; 85 86 threads_starting = nthreads; 87 88 /* create and block all threads */ 89 for (i = 0; i < nthreads; i++) { 90 CPU_ZERO(&cpu); 91 CPU_SET(i % ncpus, &cpu); 92 93 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu)) 94 err(EXIT_FAILURE, "pthread_attr_setaffinity_np"); 95 96 if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) 97 err(EXIT_FAILURE, "pthread_create"); 98 } 99 } 100 101 static void toggle_done(int sig __maybe_unused, 102 siginfo_t *info __maybe_unused, 103 void *uc __maybe_unused) 104 { 105 done = true; 106 } 107 108 int bench_futex_wake(int argc, const char **argv, 109 const char *prefix __maybe_unused) 110 { 111 int ret = 0; 112 unsigned int i, j; 113 struct sigaction act; 114 pthread_attr_t thread_attr; 115 116 argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0); 117 if (argc) { 118 usage_with_options(bench_futex_wake_usage, options); 119 exit(EXIT_FAILURE); 120 } 121 122 ncpus = sysconf(_SC_NPROCESSORS_ONLN); 123 124 sigfillset(&act.sa_mask); 125 act.sa_sigaction = toggle_done; 126 sigaction(SIGINT, &act, NULL); 127 128 if (!nthreads) 129 nthreads = ncpus; 130 131 worker = calloc(nthreads, sizeof(*worker)); 132 if (!worker) 133 err(EXIT_FAILURE, "calloc"); 134 135 if (!fshared) 136 futex_flag = FUTEX_PRIVATE_FLAG; 137 138 printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), " 139 "waking up %d at a time.\n\n", 140 getpid(), nthreads, fshared ? "shared":"private", &futex1, nwakes); 141 142 init_stats(&wakeup_stats); 143 init_stats(&waketime_stats); 144 pthread_attr_init(&thread_attr); 145 pthread_mutex_init(&thread_lock, NULL); 146 pthread_cond_init(&thread_parent, NULL); 147 pthread_cond_init(&thread_worker, NULL); 148 149 for (j = 0; j < bench_repeat && !done; j++) { 150 unsigned int nwoken = 0; 151 struct timeval start, end, runtime; 152 153 /* create, launch & block all threads */ 154 block_threads(worker, thread_attr); 155 156 /* make sure all threads are already blocked */ 157 pthread_mutex_lock(&thread_lock); 158 while (threads_starting) 159 pthread_cond_wait(&thread_parent, &thread_lock); 160 pthread_cond_broadcast(&thread_worker); 161 pthread_mutex_unlock(&thread_lock); 162 163 usleep(100000); 164 165 /* Ok, all threads are patiently blocked, start waking folks up */ 166 gettimeofday(&start, NULL); 167 while (nwoken != nthreads) 168 nwoken += futex_wake(&futex1, nwakes, futex_flag); 169 gettimeofday(&end, NULL); 170 timersub(&end, &start, &runtime); 171 172 update_stats(&wakeup_stats, nwoken); 173 update_stats(&waketime_stats, runtime.tv_usec); 174 175 if (!silent) { 176 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n", 177 j + 1, nwoken, nthreads, runtime.tv_usec/1e3); 178 } 179 180 for (i = 0; i < nthreads; i++) { 181 ret = pthread_join(worker[i], NULL); 182 if (ret) 183 err(EXIT_FAILURE, "pthread_join"); 184 } 185 186 } 187 188 /* cleanup & report results */ 189 pthread_cond_destroy(&thread_parent); 190 pthread_cond_destroy(&thread_worker); 191 pthread_mutex_destroy(&thread_lock); 192 pthread_attr_destroy(&thread_attr); 193 194 print_summary(); 195 196 free(worker); 197 return ret; 198 } 199