2 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
4 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
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.
12 #include "../util/util.h"
13 #include "../util/stat.h"
14 #include "../util/parse-options.h"
15 #include "../util/header.h"
24 /* all threads will block on the same futex */
25 static u_int32_t futex1 = 0;
28 * How many wakeups to do at a time.
29 * Default to 1 in order to make the kernel work more.
31 static unsigned int nwakes = 1;
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.
38 static unsigned int repeat = 10;
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;
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"),
55 static const char * const bench_futex_wake_usage[] = {
56 "perf bench futex wake <options>",
60 static void *workerfn(void *arg __maybe_unused)
62 pthread_mutex_lock(&thread_lock);
64 if (!threads_starting)
65 pthread_cond_signal(&thread_parent);
66 pthread_cond_wait(&thread_worker, &thread_lock);
67 pthread_mutex_unlock(&thread_lock);
69 futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
73 static void print_summary(void)
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);
79 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
83 rel_stddev_stats(waketime_stddev, waketime_avg));
86 static void block_threads(pthread_t *w,
87 pthread_attr_t thread_attr)
92 threads_starting = nthreads;
94 /* create and block all threads */
95 for (i = 0; i < nthreads; i++) {
97 CPU_SET(i % ncpus, &cpu);
99 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
100 err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
102 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
103 err(EXIT_FAILURE, "pthread_create");
107 static void toggle_done(int sig __maybe_unused,
108 siginfo_t *info __maybe_unused,
109 void *uc __maybe_unused)
114 int bench_futex_wake(int argc, const char **argv,
115 const char *prefix __maybe_unused)
119 struct sigaction act;
120 pthread_attr_t thread_attr;
122 argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
124 usage_with_options(bench_futex_wake_usage, options);
128 ncpus = sysconf(_SC_NPROCESSORS_ONLN);
130 sigfillset(&act.sa_mask);
131 act.sa_sigaction = toggle_done;
132 sigaction(SIGINT, &act, NULL);
137 worker = calloc(nthreads, sizeof(*worker));
139 err(EXIT_FAILURE, "calloc");
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);
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);
152 for (j = 0; j < repeat && !done; j++) {
153 unsigned int nwoken = 0;
154 struct timeval start, end, runtime;
156 /* create, launch & block all threads */
157 block_threads(worker, thread_attr);
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);
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);
175 update_stats(&wakeup_stats, nwoken);
176 update_stats(&waketime_stats, runtime.tv_usec);
179 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
180 j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
183 for (i = 0; i < nthreads; i++) {
184 ret = pthread_join(worker[i], NULL);
186 err(EXIT_FAILURE, "pthread_join");
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);