1 // SPDX-License-Identifier: GPL-2.0
3 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
5 * futex-requeue: Block a bunch of threads on futex1 and requeue them
6 * on futex2, N at a time.
8 * This program is particularly useful to measure the latency of nthread
9 * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
12 /* For the CLR_() macros */
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>
23 #include <internal/cpumap.h>
24 #include <perf/cpumap.h>
32 static u_int32_t futex1 = 0, futex2 = 0;
35 * How many tasks to requeue at a time.
36 * Default to 1 in order to make the kernel work more.
38 static unsigned int nrequeue = 1;
40 static 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 requeuetime_stats, requeued_stats;
45 static unsigned int threads_starting, nthreads = 0;
46 static int futex_flag = 0;
48 static const struct option options[] = {
49 OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
50 OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue 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"),
56 static const char * const bench_futex_requeue_usage[] = {
57 "perf bench futex requeue <options>",
61 static void print_summary(void)
63 double requeuetime_avg = avg_stats(&requeuetime_stats);
64 double requeuetime_stddev = stddev_stats(&requeuetime_stats);
65 unsigned int requeued_avg = avg_stats(&requeued_stats);
67 printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
70 requeuetime_avg / USEC_PER_MSEC,
71 rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
74 static void *workerfn(void *arg __maybe_unused)
76 pthread_mutex_lock(&thread_lock);
78 if (!threads_starting)
79 pthread_cond_signal(&thread_parent);
80 pthread_cond_wait(&thread_worker, &thread_lock);
81 pthread_mutex_unlock(&thread_lock);
83 futex_wait(&futex1, 0, NULL, futex_flag);
87 static void block_threads(pthread_t *w,
88 pthread_attr_t thread_attr, struct perf_cpu_map *cpu)
93 threads_starting = nthreads;
95 /* create and block all threads */
96 for (i = 0; i < nthreads; i++) {
98 CPU_SET(cpu->map[i % cpu->nr], &cpuset);
100 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
101 err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
103 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
104 err(EXIT_FAILURE, "pthread_create");
108 static void toggle_done(int sig __maybe_unused,
109 siginfo_t *info __maybe_unused,
110 void *uc __maybe_unused)
115 int bench_futex_requeue(int argc, const char **argv)
119 struct sigaction act;
120 pthread_attr_t thread_attr;
121 struct perf_cpu_map *cpu;
123 argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
127 cpu = perf_cpu_map__new(NULL);
129 err(EXIT_FAILURE, "cpu_map__new");
131 memset(&act, 0, sizeof(act));
132 sigfillset(&act.sa_mask);
133 act.sa_sigaction = toggle_done;
134 sigaction(SIGINT, &act, NULL);
139 worker = calloc(nthreads, sizeof(*worker));
141 err(EXIT_FAILURE, "calloc");
144 futex_flag = FUTEX_PRIVATE_FLAG;
146 if (nrequeue > nthreads)
149 printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
150 "%d at a time.\n\n", getpid(), nthreads,
151 fshared ? "shared":"private", &futex1, &futex2, nrequeue);
153 init_stats(&requeued_stats);
154 init_stats(&requeuetime_stats);
155 pthread_attr_init(&thread_attr);
156 pthread_mutex_init(&thread_lock, NULL);
157 pthread_cond_init(&thread_parent, NULL);
158 pthread_cond_init(&thread_worker, NULL);
160 for (j = 0; j < bench_repeat && !done; j++) {
161 unsigned int nrequeued = 0;
162 struct timeval start, end, runtime;
164 /* create, launch & block all threads */
165 block_threads(worker, thread_attr, cpu);
167 /* make sure all threads are already blocked */
168 pthread_mutex_lock(&thread_lock);
169 while (threads_starting)
170 pthread_cond_wait(&thread_parent, &thread_lock);
171 pthread_cond_broadcast(&thread_worker);
172 pthread_mutex_unlock(&thread_lock);
176 /* Ok, all threads are patiently blocked, start requeueing */
177 gettimeofday(&start, NULL);
178 while (nrequeued < nthreads) {
180 * Do not wakeup any tasks blocked on futex1, allowing
181 * us to really measure futex_wait functionality.
183 nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
184 nrequeue, futex_flag);
187 gettimeofday(&end, NULL);
188 timersub(&end, &start, &runtime);
190 update_stats(&requeued_stats, nrequeued);
191 update_stats(&requeuetime_stats, runtime.tv_usec);
194 printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
195 j + 1, nrequeued, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
198 /* everybody should be blocked on futex2, wake'em up */
199 nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
200 if (nthreads != nrequeued)
201 warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
203 for (i = 0; i < nthreads; i++) {
204 ret = pthread_join(worker[i], NULL);
206 err(EXIT_FAILURE, "pthread_join");
210 /* cleanup & report results */
211 pthread_cond_destroy(&thread_parent);
212 pthread_cond_destroy(&thread_worker);
213 pthread_mutex_destroy(&thread_lock);
214 pthread_attr_destroy(&thread_attr);
221 usage_with_options(bench_futex_requeue_usage, options);