futex-wake.c

  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/mutex.h"
 18#include "../util/stat.h"
 19#include <subcmd/parse-options.h>
 20#include <linux/compiler.h>
 21#include <linux/kernel.h>
 22#include <linux/time64.h>
 23#include <errno.h>
 24#include <perf/cpumap.h>
 25#include "bench.h"
 26#include "futex.h"
 27
 28#include <err.h>
 29#include <stdlib.h>
 30#include <sys/time.h>
 31#include <sys/mman.h>
 32
 33/* all threads will block on the same futex */
 34static u_int32_t futex1 = 0;
 35
 36static pthread_t *worker;
 37static bool done = false;
 38static struct mutex thread_lock;
 39static struct cond thread_parent, thread_worker;
 40static struct stats waketime_stats, wakeup_stats;
 41static unsigned int threads_starting;
 42static int futex_flag = 0;
 43
 44static struct bench_futex_parameters params = {
 45	.nbuckets = -1,
 46	/*
 47	 * How many wakeups to do at a time.
 48	 * Default to 1 in order to make the kernel work more.
 49	 */
 50	.nwakes  = 1,
 51};
 52
 53static const struct option options[] = {
 54	OPT_INTEGER( 'b', "buckets", &params.nbuckets, "Specify amount of hash buckets"),
 55	OPT_UINTEGER('t', "threads", &params.nthreads, "Specify amount of threads"),
 56	OPT_UINTEGER('w', "nwakes",  &params.nwakes, "Specify amount of threads to wake at once"),
 57	OPT_BOOLEAN( 's', "silent",  &params.silent, "Silent mode: do not display data/details"),
 58	OPT_BOOLEAN( 'S', "shared",  &params.fshared, "Use shared futexes instead of private ones"),
 59	OPT_BOOLEAN( 'm', "mlockall", &params.mlockall, "Lock all current and future memory"),
 60
 61	OPT_END()
 62};
 63
 64static const char * const bench_futex_wake_usage[] = {
 65	"perf bench futex wake <options>",
 66	NULL
 67};
 68
 69static void *workerfn(void *arg __maybe_unused)
 70{
 71	mutex_lock(&thread_lock);
 72	threads_starting--;
 73	if (!threads_starting)
 74		cond_signal(&thread_parent);
 75	cond_wait(&thread_worker, &thread_lock);
 76	mutex_unlock(&thread_lock);
 77
 78	while (1) {
 79		if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
 80			break;
 81	}
 82
 83	pthread_exit(NULL);
 84	return NULL;
 85}
 86
 87static void print_summary(void)
 88{
 89	double waketime_avg = avg_stats(&waketime_stats);
 90	double waketime_stddev = stddev_stats(&waketime_stats);
 91	unsigned int wakeup_avg = avg_stats(&wakeup_stats);
 92
 93	printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
 94	       wakeup_avg,
 95	       params.nthreads,
 96	       waketime_avg / USEC_PER_MSEC,
 97	       rel_stddev_stats(waketime_stddev, waketime_avg));
 98	futex_print_nbuckets(&params);
 99}
100
101static void block_threads(pthread_t *w, struct perf_cpu_map *cpu)
102{
103	cpu_set_t *cpuset;
104	unsigned int i;
105	size_t size;
106	int nrcpus = cpu__max_cpu().cpu;
107	threads_starting = params.nthreads;
108
109	cpuset = CPU_ALLOC(nrcpus);
110	BUG_ON(!cpuset);
111	size = CPU_ALLOC_SIZE(nrcpus);
112
113	/* create and block all threads */
114	for (i = 0; i < params.nthreads; i++) {
115		pthread_attr_t thread_attr;
116
117		pthread_attr_init(&thread_attr);
118		CPU_ZERO_S(size, cpuset);
119		CPU_SET_S(perf_cpu_map__cpu(cpu, i % perf_cpu_map__nr(cpu)).cpu, size, cpuset);
120
121		if (pthread_attr_setaffinity_np(&thread_attr, size, cpuset)) {
122			CPU_FREE(cpuset);
123			err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
124		}
125
126		if (pthread_create(&w[i], &thread_attr, workerfn, NULL)) {
127			CPU_FREE(cpuset);
128			err(EXIT_FAILURE, "pthread_create");
129		}
130		pthread_attr_destroy(&thread_attr);
131	}
132	CPU_FREE(cpuset);
133}
134
135static void toggle_done(int sig __maybe_unused,
136			siginfo_t *info __maybe_unused,
137			void *uc __maybe_unused)
138{
139	done = true;
140}
141
142int bench_futex_wake(int argc, const char **argv)
143{
144	int ret = 0;
145	unsigned int i, j;
146	struct sigaction act;
147	struct perf_cpu_map *cpu;
148
149	argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
150	if (argc) {
151		usage_with_options(bench_futex_wake_usage, options);
152		exit(EXIT_FAILURE);
153	}
154
155	cpu = perf_cpu_map__new_online_cpus();
156	if (!cpu)
157		err(EXIT_FAILURE, "calloc");
158
159	memset(&act, 0, sizeof(act));
160	sigfillset(&act.sa_mask);
161	act.sa_sigaction = toggle_done;
162	sigaction(SIGINT, &act, NULL);
163
164	if (params.mlockall) {
165		if (mlockall(MCL_CURRENT | MCL_FUTURE))
166			err(EXIT_FAILURE, "mlockall");
167	}
168
169	if (!params.nthreads)
170		params.nthreads = perf_cpu_map__nr(cpu);
171
172	worker = calloc(params.nthreads, sizeof(*worker));
173	if (!worker)
174		err(EXIT_FAILURE, "calloc");
175
176	if (!params.fshared)
177		futex_flag = FUTEX_PRIVATE_FLAG;
178
179	printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
180	       "waking up %d at a time.\n\n",
181	       getpid(), params.nthreads, params.fshared ? "shared":"private",
182	       &futex1, params.nwakes);
183
184	init_stats(&wakeup_stats);
185	init_stats(&waketime_stats);
186	mutex_init(&thread_lock);
187	cond_init(&thread_parent);
188	cond_init(&thread_worker);
189
190	for (j = 0; j < bench_repeat && !done; j++) {
191		unsigned int nwoken = 0;
192		struct timeval start, end, runtime;
193
194		/* create, launch & block all threads */
195		block_threads(worker, cpu);
196
197		/* make sure all threads are already blocked */
198		mutex_lock(&thread_lock);
199		while (threads_starting)
200			cond_wait(&thread_parent, &thread_lock);
201		cond_broadcast(&thread_worker);
202		mutex_unlock(&thread_lock);
203
204		usleep(100000);
205
206		/* Ok, all threads are patiently blocked, start waking folks up */
207		gettimeofday(&start, NULL);
208		while (nwoken != params.nthreads)
209			nwoken += futex_wake(&futex1,
210					     params.nwakes, futex_flag);
211		gettimeofday(&end, NULL);
212		timersub(&end, &start, &runtime);
213
214		update_stats(&wakeup_stats, nwoken);
215		update_stats(&waketime_stats, runtime.tv_usec);
216
217		if (!params.silent) {
218			printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
219			       j + 1, nwoken, params.nthreads,
220			       runtime.tv_usec / (double)USEC_PER_MSEC);
221		}
222
223		for (i = 0; i < params.nthreads; i++) {
224			ret = pthread_join(worker[i], NULL);
225			if (ret)
226				err(EXIT_FAILURE, "pthread_join");
227		}
228
229	}
230
231	/* cleanup & report results */
232	cond_destroy(&thread_parent);
233	cond_destroy(&thread_worker);
234	mutex_destroy(&thread_lock);
235
236	print_summary();
237
238	free(worker);
239	perf_cpu_map__put(cpu);
240	return ret;
241}