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Linux/tools/perf/bench/futex-wake.c

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  1 /*
  2  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
  3  *
  4  * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
  5  *
  6  * This program is particularly useful to measure the latency of nthread wakeups
  7  * in non-error situations:  all waiters are queued and all wake calls wakeup
  8  * one or more tasks, and thus the waitqueue is never empty.
  9  */
 10 
 11 /* For the CLR_() macros */
 12 #include <pthread.h>
 13 
 14 #include <signal.h>
 15 #include "../util/stat.h"
 16 #include <subcmd/parse-options.h>
 17 #include <linux/compiler.h>
 18 #include <linux/kernel.h>
 19 #include <linux/time64.h>
 20 #include <errno.h>
 21 #include "bench.h"
 22 #include "futex.h"
 23 
 24 #include <err.h>
 25 #include <stdlib.h>
 26 #include <sys/time.h>
 27 
 28 /* all threads will block on the same futex */
 29 static u_int32_t futex1 = 0;
 30 
 31 /*
 32  * How many wakeups to do at a time.
 33  * Default to 1 in order to make the kernel work more.
 34  */
 35 static unsigned int nwakes = 1;
 36 
 37 pthread_t *worker;
 38 static bool done = false, silent = false, fshared = false;
 39 static pthread_mutex_t thread_lock;
 40 static pthread_cond_t thread_parent, thread_worker;
 41 static struct stats waketime_stats, wakeup_stats;
 42 static unsigned int ncpus, threads_starting, nthreads = 0;
 43 static int futex_flag = 0;
 44 
 45 static const struct option options[] = {
 46         OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
 47         OPT_UINTEGER('w', "nwakes",  &nwakes,   "Specify amount of threads to wake at once"),
 48         OPT_BOOLEAN( 's', "silent",  &silent,   "Silent mode: do not display data/details"),
 49         OPT_BOOLEAN( 'S', "shared",  &fshared,  "Use shared futexes instead of private ones"),
 50         OPT_END()
 51 };
 52 
 53 static const char * const bench_futex_wake_usage[] = {
 54         "perf bench futex wake <options>",
 55         NULL
 56 };
 57 
 58 static void *workerfn(void *arg __maybe_unused)
 59 {
 60         pthread_mutex_lock(&thread_lock);
 61         threads_starting--;
 62         if (!threads_starting)
 63                 pthread_cond_signal(&thread_parent);
 64         pthread_cond_wait(&thread_worker, &thread_lock);
 65         pthread_mutex_unlock(&thread_lock);
 66 
 67         while (1) {
 68                 if (futex_wait(&futex1, 0, NULL, futex_flag) != EINTR)
 69                         break;
 70         }
 71 
 72         pthread_exit(NULL);
 73         return NULL;
 74 }
 75 
 76 static void print_summary(void)
 77 {
 78         double waketime_avg = avg_stats(&waketime_stats);
 79         double waketime_stddev = stddev_stats(&waketime_stats);
 80         unsigned int wakeup_avg = avg_stats(&wakeup_stats);
 81 
 82         printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
 83                wakeup_avg,
 84                nthreads,
 85                waketime_avg / USEC_PER_MSEC,
 86                rel_stddev_stats(waketime_stddev, waketime_avg));
 87 }
 88 
 89 static void block_threads(pthread_t *w,
 90                           pthread_attr_t thread_attr)
 91 {
 92         cpu_set_t cpu;
 93         unsigned int i;
 94 
 95         threads_starting = nthreads;
 96 
 97         /* create and block all threads */
 98         for (i = 0; i < nthreads; i++) {
 99                 CPU_ZERO(&cpu);
100                 CPU_SET(i % ncpus, &cpu);
101 
102                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
103                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
104 
105                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
106                         err(EXIT_FAILURE, "pthread_create");
107         }
108 }
109 
110 static void toggle_done(int sig __maybe_unused,
111                         siginfo_t *info __maybe_unused,
112                         void *uc __maybe_unused)
113 {
114         done = true;
115 }
116 
117 int bench_futex_wake(int argc, const char **argv,
118                      const char *prefix __maybe_unused)
119 {
120         int ret = 0;
121         unsigned int i, j;
122         struct sigaction act;
123         pthread_attr_t thread_attr;
124 
125         argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
126         if (argc) {
127                 usage_with_options(bench_futex_wake_usage, options);
128                 exit(EXIT_FAILURE);
129         }
130 
131         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
132         nwakes = futexbench_sanitize_numeric(nwakes);
133 
134         sigfillset(&act.sa_mask);
135         act.sa_sigaction = toggle_done;
136         sigaction(SIGINT, &act, NULL);
137 
138         if (!nthreads)
139                 nthreads = ncpus;
140         else
141                 nthreads = futexbench_sanitize_numeric(nthreads);
142 
143         worker = calloc(nthreads, sizeof(*worker));
144         if (!worker)
145                 err(EXIT_FAILURE, "calloc");
146 
147         if (!fshared)
148                 futex_flag = FUTEX_PRIVATE_FLAG;
149 
150         printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
151                "waking up %d at a time.\n\n",
152                getpid(), nthreads, fshared ? "shared":"private",  &futex1, nwakes);
153 
154         init_stats(&wakeup_stats);
155         init_stats(&waketime_stats);
156         pthread_attr_init(&thread_attr);
157         pthread_mutex_init(&thread_lock, NULL);
158         pthread_cond_init(&thread_parent, NULL);
159         pthread_cond_init(&thread_worker, NULL);
160 
161         for (j = 0; j < bench_repeat && !done; j++) {
162                 unsigned int nwoken = 0;
163                 struct timeval start, end, runtime;
164 
165                 /* create, launch & block all threads */
166                 block_threads(worker, thread_attr);
167 
168                 /* make sure all threads are already blocked */
169                 pthread_mutex_lock(&thread_lock);
170                 while (threads_starting)
171                         pthread_cond_wait(&thread_parent, &thread_lock);
172                 pthread_cond_broadcast(&thread_worker);
173                 pthread_mutex_unlock(&thread_lock);
174 
175                 usleep(100000);
176 
177                 /* Ok, all threads are patiently blocked, start waking folks up */
178                 gettimeofday(&start, NULL);
179                 while (nwoken != nthreads)
180                         nwoken += futex_wake(&futex1, nwakes, futex_flag);
181                 gettimeofday(&end, NULL);
182                 timersub(&end, &start, &runtime);
183 
184                 update_stats(&wakeup_stats, nwoken);
185                 update_stats(&waketime_stats, runtime.tv_usec);
186 
187                 if (!silent) {
188                         printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
189                                j + 1, nwoken, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
190                 }
191 
192                 for (i = 0; i < nthreads; i++) {
193                         ret = pthread_join(worker[i], NULL);
194                         if (ret)
195                                 err(EXIT_FAILURE, "pthread_join");
196                 }
197 
198         }
199 
200         /* cleanup & report results */
201         pthread_cond_destroy(&thread_parent);
202         pthread_cond_destroy(&thread_worker);
203         pthread_mutex_destroy(&thread_lock);
204         pthread_attr_destroy(&thread_attr);
205 
206         print_summary();
207 
208         free(worker);
209         return ret;
210 }
211 

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