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/*
* Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
*
* futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
*
* This program is particularly useful to measure the latency of nthread wakeups
* in non-error situations: all waiters are queued and all wake calls wakeup
* one or more tasks, and thus the waitqueue is never empty.
*/
#include "../perf.h"
#include "../util/util.h"
#include "../util/stat.h"
#include "../util/parse-options.h"
#include "../util/header.h"
#include "bench.h"
#include "futex.h"
#include <err.h>
#include <stdlib.h>
#include <sys/time.h>
#include <pthread.h>
/* all threads will block on the same futex */
static u_int32_t futex1 = 0;
/*
* How many wakeups to do at a time.
* Default to 1 in order to make the kernel work more.
*/
static unsigned int nwakes = 1;
/*
* There can be significant variance from run to run,
* the more repeats, the more exact the overall avg and
* the better idea of the futex latency.
*/
static unsigned int repeat = 10;
pthread_t *worker;
static bool done = 0, silent = 0;
static pthread_mutex_t thread_lock;
static pthread_cond_t thread_parent, thread_worker;
static struct stats waketime_stats, wakeup_stats;
static unsigned int ncpus, threads_starting, nthreads = 0;
static const struct option options[] = {
OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"),
OPT_UINTEGER('r', "repeat", &repeat, "Specify amount of times to repeat the run"),
OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
OPT_END()
};
static const char * const bench_futex_wake_usage[] = {
"perf bench futex wake <options>",
NULL
};
static void *workerfn(void *arg __maybe_unused)
{
pthread_mutex_lock(&thread_lock);
threads_starting--;
if (!threads_starting)
pthread_cond_signal(&thread_parent);
pthread_cond_wait(&thread_worker, &thread_lock);
pthread_mutex_unlock(&thread_lock);
futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
return NULL;
}
static void print_summary(void)
{
double waketime_avg = avg_stats(&waketime_stats);
double waketime_stddev = stddev_stats(&waketime_stats);
unsigned int wakeup_avg = avg_stats(&wakeup_stats);
printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
wakeup_avg,
nthreads,
waketime_avg/1e3,
rel_stddev_stats(waketime_stddev, waketime_avg));
}
static void block_threads(pthread_t *w,
pthread_attr_t thread_attr)
{
cpu_set_t cpu;
unsigned int i;
threads_starting = nthreads;
/* create and block all threads */
for (i = 0; i < nthreads; i++) {
CPU_ZERO(&cpu);
CPU_SET(i % ncpus, &cpu);
if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
err(EXIT_FAILURE, "pthread_create");
}
}
static void toggle_done(int sig __maybe_unused,
siginfo_t *info __maybe_unused,
void *uc __maybe_unused)
{
done = true;
}
int bench_futex_wake(int argc, const char **argv,
const char *prefix __maybe_unused)
{
int ret = 0;
unsigned int i, j;
struct sigaction act;
pthread_attr_t thread_attr;
argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
if (argc) {
usage_with_options(bench_futex_wake_usage, options);
exit(EXIT_FAILURE);
}
ncpus = sysconf(_SC_NPROCESSORS_ONLN);
sigfillset(&act.sa_mask);
act.sa_sigaction = toggle_done;
sigaction(SIGINT, &act, NULL);
if (!nthreads)
nthreads = ncpus;
worker = calloc(nthreads, sizeof(*worker));
if (!worker)
err(EXIT_FAILURE, "calloc");
printf("Run summary [PID %d]: blocking on %d threads (at futex %p), "
"waking up %d at a time.\n\n",
getpid(), nthreads, &futex1, nwakes);
init_stats(&wakeup_stats);
init_stats(&waketime_stats);
pthread_attr_init(&thread_attr);
pthread_mutex_init(&thread_lock, NULL);
pthread_cond_init(&thread_parent, NULL);
pthread_cond_init(&thread_worker, NULL);
for (j = 0; j < repeat && !done; j++) {
unsigned int nwoken = 0;
struct timeval start, end, runtime;
/* create, launch & block all threads */
block_threads(worker, thread_attr);
/* make sure all threads are already blocked */
pthread_mutex_lock(&thread_lock);
while (threads_starting)
pthread_cond_wait(&thread_parent, &thread_lock);
pthread_cond_broadcast(&thread_worker);
pthread_mutex_unlock(&thread_lock);
usleep(100000);
/* Ok, all threads are patiently blocked, start waking folks up */
gettimeofday(&start, NULL);
while (nwoken != nthreads)
nwoken += futex_wake(&futex1, nwakes, FUTEX_PRIVATE_FLAG);
gettimeofday(&end, NULL);
timersub(&end, &start, &runtime);
update_stats(&wakeup_stats, nwoken);
update_stats(&waketime_stats, runtime.tv_usec);
if (!silent) {
printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
}
for (i = 0; i < nthreads; i++) {
ret = pthread_join(worker[i], NULL);
if (ret)
err(EXIT_FAILURE, "pthread_join");
}
}
/* cleanup & report results */
pthread_cond_destroy(&thread_parent);
pthread_cond_destroy(&thread_worker);
pthread_mutex_destroy(&thread_lock);
pthread_attr_destroy(&thread_attr);
print_summary();
free(worker);
return ret;
}
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