![Davidlohr Bueso](/assets/img/avatar_default.png)
Block a bunch of threads on a futex and wake them 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. An example run: $ perf bench futex wake -t 512 -r 100 Run summary [PID 27823]: blocking on 512 threads (at futex 0x7e10d4), waking up 1 at a time. [Run 1]: Wokeup 512 of 512 threads in 6.0080 ms [Run 2]: Wokeup 512 of 512 threads in 5.2280 ms [Run 3]: Wokeup 512 of 512 threads in 4.8300 ms ... [Run 100]: Wokeup 512 of 512 threads in 5.0100 ms Wokeup 512 of 512 threads in 5.0109 ms (+-2.25%) Signed-off-by: Davidlohr Bueso <davidlohr@hp.com> Acked-by: Darren Hart <dvhart@linux.intel.com> Cc: Aswin Chandramouleeswaran <aswin@hp.com> Cc: Darren Hart <dvhart@linux.intel.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jason Low <jason.low2@hp.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Waiman Long <Waiman.Long@hp.com> Link: http://lkml.kernel.org/r/1387081917-9102-3-git-send-email-davidlohr@hp.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
202 lines
5.3 KiB
C
202 lines
5.3 KiB
C
/*
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* Copyright (C) 2013 Davidlohr Bueso <davidlohr@hp.com>
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*
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* futex-wake: Block a bunch of threads on a futex and wake'em up, N at a time.
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*
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* This program is particularly useful to measure the latency of nthread wakeups
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* in non-error situations: all waiters are queued and all wake calls wakeup
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* one or more tasks, and thus the waitqueue is never empty.
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*/
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#include "../perf.h"
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#include "../util/util.h"
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#include "../util/stat.h"
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#include "../util/parse-options.h"
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#include "../util/header.h"
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#include "bench.h"
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#include "futex.h"
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#include <err.h>
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#include <stdlib.h>
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#include <sys/time.h>
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#include <pthread.h>
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/* all threads will block on the same futex */
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static u_int32_t futex1 = 0;
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/*
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* How many wakeups to do at a time.
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* Default to 1 in order to make the kernel work more.
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*/
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static unsigned int nwakes = 1;
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/*
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* There can be significant variance from run to run,
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* the more repeats, the more exact the overall avg and
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* the better idea of the futex latency.
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*/
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static unsigned int repeat = 10;
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pthread_t *worker;
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static bool done = 0, silent = 0;
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static pthread_mutex_t thread_lock;
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static pthread_cond_t thread_parent, thread_worker;
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static struct stats waketime_stats, wakeup_stats;
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static unsigned int ncpus, threads_starting, nthreads = 0;
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static const struct option options[] = {
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OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
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OPT_UINTEGER('w', "nwakes", &nwakes, "Specify amount of threads to wake at once"),
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OPT_UINTEGER('r', "repeat", &repeat, "Specify amount of times to repeat the run"),
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OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
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OPT_END()
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};
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static const char * const bench_futex_wake_usage[] = {
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"perf bench futex wake <options>",
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NULL
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};
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static void *workerfn(void *arg __maybe_unused)
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{
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pthread_mutex_lock(&thread_lock);
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threads_starting--;
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if (!threads_starting)
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pthread_cond_signal(&thread_parent);
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pthread_cond_wait(&thread_worker, &thread_lock);
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pthread_mutex_unlock(&thread_lock);
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futex_wait(&futex1, 0, NULL, FUTEX_PRIVATE_FLAG);
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return NULL;
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}
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static void print_summary(void)
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{
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double waketime_avg = avg_stats(&waketime_stats);
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double waketime_stddev = stddev_stats(&waketime_stats);
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unsigned int wakeup_avg = avg_stats(&wakeup_stats);
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printf("Wokeup %d of %d threads in %.4f ms (+-%.2f%%)\n",
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wakeup_avg,
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nthreads,
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waketime_avg/1e3,
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rel_stddev_stats(waketime_stddev, waketime_avg));
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}
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static void block_threads(pthread_t *w,
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pthread_attr_t thread_attr)
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{
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cpu_set_t cpu;
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unsigned int i;
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threads_starting = nthreads;
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/* create and block all threads */
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for (i = 0; i < nthreads; i++) {
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CPU_ZERO(&cpu);
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CPU_SET(i % ncpus, &cpu);
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if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpu))
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err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
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if (pthread_create(&w[i], &thread_attr, workerfn, NULL))
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err(EXIT_FAILURE, "pthread_create");
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}
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}
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static void toggle_done(int sig __maybe_unused,
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siginfo_t *info __maybe_unused,
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void *uc __maybe_unused)
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{
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done = true;
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}
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int bench_futex_wake(int argc, const char **argv,
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const char *prefix __maybe_unused)
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{
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int ret = 0;
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unsigned int i, j;
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struct sigaction act;
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pthread_attr_t thread_attr;
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argc = parse_options(argc, argv, options, bench_futex_wake_usage, 0);
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if (argc) {
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usage_with_options(bench_futex_wake_usage, options);
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exit(EXIT_FAILURE);
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}
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ncpus = sysconf(_SC_NPROCESSORS_ONLN);
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sigfillset(&act.sa_mask);
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act.sa_sigaction = toggle_done;
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sigaction(SIGINT, &act, NULL);
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if (!nthreads)
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nthreads = ncpus;
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worker = calloc(nthreads, sizeof(*worker));
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if (!worker)
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err(EXIT_FAILURE, "calloc");
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printf("Run summary [PID %d]: blocking on %d threads (at futex %p), "
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"waking up %d at a time.\n\n",
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getpid(), nthreads, &futex1, nwakes);
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init_stats(&wakeup_stats);
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init_stats(&waketime_stats);
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pthread_attr_init(&thread_attr);
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pthread_mutex_init(&thread_lock, NULL);
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pthread_cond_init(&thread_parent, NULL);
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pthread_cond_init(&thread_worker, NULL);
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for (j = 0; j < repeat && !done; j++) {
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unsigned int nwoken = 0;
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struct timeval start, end, runtime;
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/* create, launch & block all threads */
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block_threads(worker, thread_attr);
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/* make sure all threads are already blocked */
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pthread_mutex_lock(&thread_lock);
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while (threads_starting)
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pthread_cond_wait(&thread_parent, &thread_lock);
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pthread_cond_broadcast(&thread_worker);
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pthread_mutex_unlock(&thread_lock);
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usleep(100000);
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/* Ok, all threads are patiently blocked, start waking folks up */
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gettimeofday(&start, NULL);
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while (nwoken != nthreads)
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nwoken += futex_wake(&futex1, nwakes, FUTEX_PRIVATE_FLAG);
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gettimeofday(&end, NULL);
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timersub(&end, &start, &runtime);
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update_stats(&wakeup_stats, nwoken);
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update_stats(&waketime_stats, runtime.tv_usec);
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if (!silent) {
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printf("[Run %d]: Wokeup %d of %d threads in %.4f ms\n",
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j + 1, nwoken, nthreads, runtime.tv_usec/1e3);
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}
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for (i = 0; i < nthreads; i++) {
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ret = pthread_join(worker[i], NULL);
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if (ret)
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err(EXIT_FAILURE, "pthread_join");
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}
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}
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/* cleanup & report results */
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pthread_cond_destroy(&thread_parent);
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pthread_cond_destroy(&thread_worker);
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pthread_mutex_destroy(&thread_lock);
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pthread_attr_destroy(&thread_attr);
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print_summary();
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free(worker);
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return ret;
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}
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