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