2 * Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
4 * futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
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.
11 /* For the CLR_() macros */
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>
28 /* all threads will block on the same futex */
29 static u_int32_t futex1
= 0;
32 * How many wakeups to do at a time.
33 * Default to 1 in order to make the kernel work more.
35 static unsigned int nwakes
= 1;
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;
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"),
53 static const char * const bench_futex_wake_usage
[] = {
54 "perf bench futex wake <options>",
58 static void *workerfn(void *arg __maybe_unused
)
60 pthread_mutex_lock(&thread_lock
);
62 if (!threads_starting
)
63 pthread_cond_signal(&thread_parent
);
64 pthread_cond_wait(&thread_worker
, &thread_lock
);
65 pthread_mutex_unlock(&thread_lock
);
68 if (futex_wait(&futex1
, 0, NULL
, futex_flag
) != EINTR
)
76 static void print_summary(void)
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
);
82 printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
85 waketime_avg
/ USEC_PER_MSEC
,
86 rel_stddev_stats(waketime_stddev
, waketime_avg
));
89 static void block_threads(pthread_t
*w
,
90 pthread_attr_t thread_attr
)
95 threads_starting
= nthreads
;
97 /* create and block all threads */
98 for (i
= 0; i
< nthreads
; i
++) {
100 CPU_SET(i
% ncpus
, &cpu
);
102 if (pthread_attr_setaffinity_np(&thread_attr
, sizeof(cpu_set_t
), &cpu
))
103 err(EXIT_FAILURE
, "pthread_attr_setaffinity_np");
105 if (pthread_create(&w
[i
], &thread_attr
, workerfn
, NULL
))
106 err(EXIT_FAILURE
, "pthread_create");
110 static void toggle_done(int sig __maybe_unused
,
111 siginfo_t
*info __maybe_unused
,
112 void *uc __maybe_unused
)
117 int bench_futex_wake(int argc
, const char **argv
,
118 const char *prefix __maybe_unused
)
122 struct sigaction act
;
123 pthread_attr_t thread_attr
;
125 argc
= parse_options(argc
, argv
, options
, bench_futex_wake_usage
, 0);
127 usage_with_options(bench_futex_wake_usage
, options
);
131 ncpus
= sysconf(_SC_NPROCESSORS_ONLN
);
133 sigfillset(&act
.sa_mask
);
134 act
.sa_sigaction
= toggle_done
;
135 sigaction(SIGINT
, &act
, NULL
);
140 worker
= calloc(nthreads
, sizeof(*worker
));
142 err(EXIT_FAILURE
, "calloc");
145 futex_flag
= FUTEX_PRIVATE_FLAG
;
147 printf("Run summary [PID %d]: blocking on %d threads (at [%s] futex %p), "
148 "waking up %d at a time.\n\n",
149 getpid(), nthreads
, fshared
? "shared":"private", &futex1
, nwakes
);
151 init_stats(&wakeup_stats
);
152 init_stats(&waketime_stats
);
153 pthread_attr_init(&thread_attr
);
154 pthread_mutex_init(&thread_lock
, NULL
);
155 pthread_cond_init(&thread_parent
, NULL
);
156 pthread_cond_init(&thread_worker
, NULL
);
158 for (j
= 0; j
< bench_repeat
&& !done
; j
++) {
159 unsigned int nwoken
= 0;
160 struct timeval start
, end
, runtime
;
162 /* create, launch & block all threads */
163 block_threads(worker
, thread_attr
);
165 /* make sure all threads are already blocked */
166 pthread_mutex_lock(&thread_lock
);
167 while (threads_starting
)
168 pthread_cond_wait(&thread_parent
, &thread_lock
);
169 pthread_cond_broadcast(&thread_worker
);
170 pthread_mutex_unlock(&thread_lock
);
174 /* Ok, all threads are patiently blocked, start waking folks up */
175 gettimeofday(&start
, NULL
);
176 while (nwoken
!= nthreads
)
177 nwoken
+= futex_wake(&futex1
, nwakes
, futex_flag
);
178 gettimeofday(&end
, NULL
);
179 timersub(&end
, &start
, &runtime
);
181 update_stats(&wakeup_stats
, nwoken
);
182 update_stats(&waketime_stats
, runtime
.tv_usec
);
185 printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
186 j
+ 1, nwoken
, nthreads
, runtime
.tv_usec
/ (double)USEC_PER_MSEC
);
189 for (i
= 0; i
< nthreads
; i
++) {
190 ret
= pthread_join(worker
[i
], NULL
);
192 err(EXIT_FAILURE
, "pthread_join");
197 /* cleanup & report results */
198 pthread_cond_destroy(&thread_parent
);
199 pthread_cond_destroy(&thread_worker
);
200 pthread_mutex_destroy(&thread_lock
);
201 pthread_attr_destroy(&thread_attr
);