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 */
34 static u_int32_t futex1 = 0;
35
36 static pthread_t *worker;
37 static bool done = false;
38 static struct mutex thread_lock;
39 static struct cond thread_parent, thread_worker;
40 static struct stats waketime_stats, wakeup_stats;
41 static unsigned int threads_starting;
42 static int futex_flag = 0;
43
44 static 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
52 static const struct option options[] = {
53 OPT_UINTEGER('t', "threads", ¶ms.nthreads, "Specify amount of threads"),
54 OPT_UINTEGER('w', "nwakes", ¶ms.nwakes, "Specify amount of threads to wake at once"),
55 OPT_BOOLEAN( 's', "silent", ¶ms.silent, "Silent mode: do not display data/details"),
56 OPT_BOOLEAN( 'S', "shared", ¶ms.fshared, "Use shared futexes instead of private ones"),
57 OPT_BOOLEAN( 'm', "mlockall", ¶ms.mlockall, "Lock all current and future memory"),
58
59 OPT_END()
60 };
61
62 static const char * const bench_futex_wake_usage[] = {
63 "perf bench futex wake <options>",
64 NULL
65 };
66
67 static 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
85 static 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
98 static 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 = cpu__max_cpu().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
132 static void toggle_done(int sig __maybe_unused,
133 siginfo_t *info __maybe_unused,
134 void *uc __maybe_unused)
135 {
136 done = true;
137 }
138
139 int 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
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