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(cnd: &thread_parent);
75 cond_wait(cnd: &thread_worker, mtx: &thread_lock);
76 mutex_unlock(lock: &thread_lock);
77
78 while (1) {
79 if (futex_wait(uaddr: &futex1, val: 0, NULL, opflags: 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(stats: &waketime_stats);
90 double waketime_stddev = stddev_stats(stats: &waketime_stats);
91 unsigned int wakeup_avg = avg_stats(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(stddev: waketime_stddev, avg: waketime_avg));
98 futex_print_nbuckets(params: &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(stats: &wakeup_stats);
185 init_stats(stats: &waketime_stats);
186 mutex_init(&thread_lock);
187 cond_init(cnd: &thread_parent);
188 cond_init(cnd: &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(cnd: &thread_parent, mtx: &thread_lock);
201 cond_broadcast(cnd: &thread_worker);
202 mutex_unlock(lock: &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(uaddr: &futex1,
210 nr_wake: params.nwakes, opflags: futex_flag);
211 gettimeofday(&end, NULL);
212 timersub(&end, &start, &runtime);
213
214 update_stats(stats: &wakeup_stats, val: nwoken);
215 update_stats(stats: &waketime_stats, val: 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(cnd: &thread_parent);
233 cond_destroy(cnd: &thread_worker);
234 mutex_destroy(lock: &thread_lock);
235
236 print_summary();
237
238 free(worker);
239 perf_cpu_map__put(cpu);
240 return ret;
241}
242

source code of linux/tools/perf/bench/futex-wake.c