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

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  1 /*
  2  * Copyright (C) 2013  Davidlohr Bueso <davidlohr@hp.com>
  3  *
  4  * futex-requeue: Block a bunch of threads on futex1 and requeue them
  5  *                on futex2, N at a time.
  6  *
  7  * This program is particularly useful to measure the latency of nthread
  8  * requeues without waking up any tasks -- thus mimicking a regular futex_wait.
  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 static u_int32_t futex1 = 0, futex2 = 0;
 29 
 30 /*
 31  * How many tasks to requeue at a time.
 32  * Default to 1 in order to make the kernel work more.
 33  */
 34 static unsigned int nrequeue = 1;
 35 
 36 static pthread_t *worker;
 37 static bool done = false, silent = false, fshared = false;
 38 static pthread_mutex_t thread_lock;
 39 static pthread_cond_t thread_parent, thread_worker;
 40 static struct stats requeuetime_stats, requeued_stats;
 41 static unsigned int ncpus, threads_starting, nthreads = 0;
 42 static int futex_flag = 0;
 43 
 44 static const struct option options[] = {
 45         OPT_UINTEGER('t', "threads",  &nthreads, "Specify amount of threads"),
 46         OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue at once"),
 47         OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
 48         OPT_BOOLEAN( 'S', "shared",   &fshared,  "Use shared futexes instead of private ones"),
 49         OPT_END()
 50 };
 51 
 52 static const char * const bench_futex_requeue_usage[] = {
 53         "perf bench futex requeue <options>",
 54         NULL
 55 };
 56 
 57 static void print_summary(void)
 58 {
 59         double requeuetime_avg = avg_stats(&requeuetime_stats);
 60         double requeuetime_stddev = stddev_stats(&requeuetime_stats);
 61         unsigned int requeued_avg = avg_stats(&requeued_stats);
 62 
 63         printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
 64                requeued_avg,
 65                nthreads,
 66                requeuetime_avg / USEC_PER_MSEC,
 67                rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
 68 }
 69 
 70 static void *workerfn(void *arg __maybe_unused)
 71 {
 72         pthread_mutex_lock(&thread_lock);
 73         threads_starting--;
 74         if (!threads_starting)
 75                 pthread_cond_signal(&thread_parent);
 76         pthread_cond_wait(&thread_worker, &thread_lock);
 77         pthread_mutex_unlock(&thread_lock);
 78 
 79         futex_wait(&futex1, 0, NULL, futex_flag);
 80         return NULL;
 81 }
 82 
 83 static void block_threads(pthread_t *w,
 84                           pthread_attr_t thread_attr)
 85 {
 86         cpu_set_t cpu;
 87         unsigned int i;
 88 
 89         threads_starting = nthreads;
 90 
 91         /* create and block all threads */
 92         for (i = 0; i < nthreads; i++) {
 93                 CPU_ZERO(&cpu);
 94                 CPU_SET(i % ncpus, &cpu);
 95 
 96                 if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
 97                         err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
 98 
 99                 if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
100                         err(EXIT_FAILURE, "pthread_create");
101         }
102 }
103 
104 static void toggle_done(int sig __maybe_unused,
105                         siginfo_t *info __maybe_unused,
106                         void *uc __maybe_unused)
107 {
108         done = true;
109 }
110 
111 int bench_futex_requeue(int argc, const char **argv,
112                         const char *prefix __maybe_unused)
113 {
114         int ret = 0;
115         unsigned int i, j;
116         struct sigaction act;
117         pthread_attr_t thread_attr;
118 
119         argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
120         if (argc)
121                 goto err;
122 
123         ncpus = sysconf(_SC_NPROCESSORS_ONLN);
124 
125         sigfillset(&act.sa_mask);
126         act.sa_sigaction = toggle_done;
127         sigaction(SIGINT, &act, NULL);
128 
129         if (!nthreads)
130                 nthreads = ncpus;
131 
132         worker = calloc(nthreads, sizeof(*worker));
133         if (!worker)
134                 err(EXIT_FAILURE, "calloc");
135 
136         if (!fshared)
137                 futex_flag = FUTEX_PRIVATE_FLAG;
138 
139         if (nrequeue > nthreads)
140                 nrequeue = nthreads;
141 
142         printf("Run summary [PID %d]: Requeuing %d threads (from [%s] %p to %p), "
143                "%d at a time.\n\n",  getpid(), nthreads,
144                fshared ? "shared":"private", &futex1, &futex2, nrequeue);
145 
146         init_stats(&requeued_stats);
147         init_stats(&requeuetime_stats);
148         pthread_attr_init(&thread_attr);
149         pthread_mutex_init(&thread_lock, NULL);
150         pthread_cond_init(&thread_parent, NULL);
151         pthread_cond_init(&thread_worker, NULL);
152 
153         for (j = 0; j < bench_repeat && !done; j++) {
154                 unsigned int nrequeued = 0;
155                 struct timeval start, end, runtime;
156 
157                 /* create, launch & block all threads */
158                 block_threads(worker, thread_attr);
159 
160                 /* make sure all threads are already blocked */
161                 pthread_mutex_lock(&thread_lock);
162                 while (threads_starting)
163                         pthread_cond_wait(&thread_parent, &thread_lock);
164                 pthread_cond_broadcast(&thread_worker);
165                 pthread_mutex_unlock(&thread_lock);
166 
167                 usleep(100000);
168 
169                 /* Ok, all threads are patiently blocked, start requeueing */
170                 gettimeofday(&start, NULL);
171                 while (nrequeued < nthreads) {
172                         /*
173                          * Do not wakeup any tasks blocked on futex1, allowing
174                          * us to really measure futex_wait functionality.
175                          */
176                         nrequeued += futex_cmp_requeue(&futex1, 0, &futex2, 0,
177                                                        nrequeue, futex_flag);
178                 }
179 
180                 gettimeofday(&end, NULL);
181                 timersub(&end, &start, &runtime);
182 
183                 update_stats(&requeued_stats, nrequeued);
184                 update_stats(&requeuetime_stats, runtime.tv_usec);
185 
186                 if (!silent) {
187                         printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
188                                j + 1, nrequeued, nthreads, runtime.tv_usec / (double)USEC_PER_MSEC);
189                 }
190 
191                 /* everybody should be blocked on futex2, wake'em up */
192                 nrequeued = futex_wake(&futex2, nrequeued, futex_flag);
193                 if (nthreads != nrequeued)
194                         warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
195 
196                 for (i = 0; i < nthreads; i++) {
197                         ret = pthread_join(worker[i], NULL);
198                         if (ret)
199                                 err(EXIT_FAILURE, "pthread_join");
200                 }
201         }
202 
203         /* cleanup & report results */
204         pthread_cond_destroy(&thread_parent);
205         pthread_cond_destroy(&thread_worker);
206         pthread_mutex_destroy(&thread_lock);
207         pthread_attr_destroy(&thread_attr);
208 
209         print_summary();
210 
211         free(worker);
212         return ret;
213 err:
214         usage_with_options(bench_futex_requeue_usage, options);
215         exit(EXIT_FAILURE);
216 }
217 

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