xref: /openbmc/linux/tools/perf/bench/futex-requeue.c (revision b34e08d5)
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 #include "../perf.h"
12 #include "../util/util.h"
13 #include "../util/stat.h"
14 #include "../util/parse-options.h"
15 #include "../util/header.h"
16 #include "bench.h"
17 #include "futex.h"
18 
19 #include <err.h>
20 #include <stdlib.h>
21 #include <sys/time.h>
22 #include <pthread.h>
23 
24 static u_int32_t futex1 = 0, futex2 = 0;
25 
26 /*
27  * How many tasks to requeue at a time.
28  * Default to 1 in order to make the kernel work more.
29  */
30 static unsigned int nrequeue = 1;
31 
32 /*
33  * There can be significant variance from run to run,
34  * the more repeats, the more exact the overall avg and
35  * the better idea of the futex latency.
36  */
37 static unsigned int repeat = 10;
38 
39 static pthread_t *worker;
40 static bool done = 0, silent = 0;
41 static pthread_mutex_t thread_lock;
42 static pthread_cond_t thread_parent, thread_worker;
43 static struct stats requeuetime_stats, requeued_stats;
44 static unsigned int ncpus, threads_starting, nthreads = 0;
45 
46 static const struct option options[] = {
47 	OPT_UINTEGER('t', "threads",  &nthreads, "Specify amount of threads"),
48 	OPT_UINTEGER('q', "nrequeue", &nrequeue, "Specify amount of threads to requeue at once"),
49 	OPT_UINTEGER('r', "repeat",   &repeat,   "Specify amount of times to repeat the run"),
50 	OPT_BOOLEAN( 's', "silent",   &silent,   "Silent mode: do not display data/details"),
51 	OPT_END()
52 };
53 
54 static const char * const bench_futex_requeue_usage[] = {
55 	"perf bench futex requeue <options>",
56 	NULL
57 };
58 
59 static void print_summary(void)
60 {
61 	double requeuetime_avg = avg_stats(&requeuetime_stats);
62 	double requeuetime_stddev = stddev_stats(&requeuetime_stats);
63 	unsigned int requeued_avg = avg_stats(&requeued_stats);
64 
65 	printf("Requeued %d of %d threads in %.4f ms (+-%.2f%%)\n",
66 	       requeued_avg,
67 	       nthreads,
68 	       requeuetime_avg/1e3,
69 	       rel_stddev_stats(requeuetime_stddev, requeuetime_avg));
70 }
71 
72 static void *workerfn(void *arg __maybe_unused)
73 {
74 	pthread_mutex_lock(&thread_lock);
75 	threads_starting--;
76 	if (!threads_starting)
77 		pthread_cond_signal(&thread_parent);
78 	pthread_cond_wait(&thread_worker, &thread_lock);
79 	pthread_mutex_unlock(&thread_lock);
80 
81 	futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
82 	return NULL;
83 }
84 
85 static void block_threads(pthread_t *w,
86 			  pthread_attr_t thread_attr)
87 {
88 	cpu_set_t cpu;
89 	unsigned int i;
90 
91 	threads_starting = nthreads;
92 
93 	/* create and block all threads */
94 	for (i = 0; i < nthreads; i++) {
95 		CPU_ZERO(&cpu);
96 		CPU_SET(i % ncpus, &cpu);
97 
98 		if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
99 			err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
100 
101 		if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
102 			err(EXIT_FAILURE, "pthread_create");
103 	}
104 }
105 
106 static void toggle_done(int sig __maybe_unused,
107 			siginfo_t *info __maybe_unused,
108 			void *uc __maybe_unused)
109 {
110 	done = true;
111 }
112 
113 int bench_futex_requeue(int argc, const char **argv,
114 			const char *prefix __maybe_unused)
115 {
116 	int ret = 0;
117 	unsigned int i, j;
118 	struct sigaction act;
119 	pthread_attr_t thread_attr;
120 
121 	argc = parse_options(argc, argv, options, bench_futex_requeue_usage, 0);
122 	if (argc)
123 		goto err;
124 
125 	ncpus = sysconf(_SC_NPROCESSORS_ONLN);
126 
127 	sigfillset(&act.sa_mask);
128 	act.sa_sigaction = toggle_done;
129 	sigaction(SIGINT, &act, NULL);
130 
131 	if (!nthreads)
132 		nthreads = ncpus;
133 
134 	worker = calloc(nthreads, sizeof(*worker));
135 	if (!worker)
136 		err(EXIT_FAILURE, "calloc");
137 
138 	printf("Run summary [PID %d]: Requeuing %d threads (from %p to %p), "
139 	       "%d at a time.\n\n",
140 	       getpid(), nthreads, &futex1, &futex2, nrequeue);
141 
142 	init_stats(&requeued_stats);
143 	init_stats(&requeuetime_stats);
144 	pthread_attr_init(&thread_attr);
145 	pthread_mutex_init(&thread_lock, NULL);
146 	pthread_cond_init(&thread_parent, NULL);
147 	pthread_cond_init(&thread_worker, NULL);
148 
149 	for (j = 0; j < repeat && !done; j++) {
150 		unsigned int nrequeued = 0;
151 		struct timeval start, end, runtime;
152 
153 		/* create, launch & block all threads */
154 		block_threads(worker, thread_attr);
155 
156 		/* make sure all threads are already blocked */
157 		pthread_mutex_lock(&thread_lock);
158 		while (threads_starting)
159 			pthread_cond_wait(&thread_parent, &thread_lock);
160 		pthread_cond_broadcast(&thread_worker);
161 		pthread_mutex_unlock(&thread_lock);
162 
163 		usleep(100000);
164 
165 		/* Ok, all threads are patiently blocked, start requeueing */
166 		gettimeofday(&start, NULL);
167 		for (nrequeued = 0; nrequeued < nthreads; nrequeued += nrequeue)
168 			/*
169 			 * Do not wakeup any tasks blocked on futex1, allowing
170 			 * us to really measure futex_wait functionality.
171 			 */
172 			futex_cmp_requeue(&futex1, 0, &futex2, 0, nrequeue,
173 					  FUTEX_PRIVATE_FLAG);
174 		gettimeofday(&end, NULL);
175 		timersub(&end, &start, &runtime);
176 
177 		update_stats(&requeued_stats, nrequeued);
178 		update_stats(&requeuetime_stats, runtime.tv_usec);
179 
180 		if (!silent) {
181 			printf("[Run %d]: Requeued %d of %d threads in %.4f ms\n",
182 			       j + 1, nrequeued, nthreads, runtime.tv_usec/1e3);
183 		}
184 
185 		/* everybody should be blocked on futex2, wake'em up */
186 		nrequeued = futex_wake(&futex2, nthreads, FUTEX_PRIVATE_FLAG);
187 		if (nthreads != nrequeued)
188 			warnx("couldn't wakeup all tasks (%d/%d)", nrequeued, nthreads);
189 
190 		for (i = 0; i < nthreads; i++) {
191 			ret = pthread_join(worker[i], NULL);
192 			if (ret)
193 				err(EXIT_FAILURE, "pthread_join");
194 		}
195 
196 	}
197 
198 	/* cleanup & report results */
199 	pthread_cond_destroy(&thread_parent);
200 	pthread_cond_destroy(&thread_worker);
201 	pthread_mutex_destroy(&thread_lock);
202 	pthread_attr_destroy(&thread_attr);
203 
204 	print_summary();
205 
206 	free(worker);
207 	return ret;
208 err:
209 	usage_with_options(bench_futex_requeue_usage, options);
210 	exit(EXIT_FAILURE);
211 }
212