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Waker threads in the futex wake-parallel benchmark are started by a loop using pthread_create(). However, there is no synchronization for when the waker threads wake the waiting threads. Comparison of the waker threads' measurement timestamps show they are not all running concurrently because older waker threads finish their task before newer waker threads even start. This patch uses a barrier to better synchronize the waker threads. Signed-off-by: James Yang <james.yang@arm.com Cc: Kim Phillips <kim.phillips@arm.com> Link: http://lkml.kernel.org/r/20171127042101.3659-4-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dave@stgolabs.net> [ Disable the wake-parallel test for systems without pthread_barrier_t ] Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
324 lines
8.6 KiB
C
324 lines
8.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright (C) 2015 Davidlohr Bueso.
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*
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* Block a bunch of threads and let parallel waker threads wakeup an
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* equal amount of them. The program output reflects the avg latency
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* for each individual thread to service its share of work. Ultimately
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* it can be used to measure futex_wake() changes.
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*/
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#include "bench.h"
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#include <linux/compiler.h>
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#include "../util/debug.h"
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#ifndef HAVE_PTHREAD_BARRIER
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int bench_futex_wake_parallel(int argc __maybe_unused, const char **argv __maybe_unused)
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{
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pr_err("%s: pthread_barrier_t unavailable, disabling this test...\n", __func__);
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return 0;
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}
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#else /* HAVE_PTHREAD_BARRIER */
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/* For the CLR_() macros */
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#include <string.h>
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#include <pthread.h>
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#include <signal.h>
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#include "../util/stat.h"
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#include <subcmd/parse-options.h>
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#include <linux/kernel.h>
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#include <linux/time64.h>
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#include <errno.h>
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#include "futex.h"
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#include "cpumap.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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struct thread_data {
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pthread_t worker;
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unsigned int nwoken;
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struct timeval runtime;
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};
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static unsigned int nwakes = 1;
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/* all threads will block on the same futex -- hash bucket chaos ;) */
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static u_int32_t futex = 0;
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static pthread_t *blocked_worker;
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static bool done = false, silent = false, fshared = false;
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static unsigned int nblocked_threads = 0, nwaking_threads = 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 pthread_barrier_t barrier;
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static struct stats waketime_stats, wakeup_stats;
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static unsigned int threads_starting;
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static int futex_flag = 0;
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static const struct option options[] = {
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OPT_UINTEGER('t', "threads", &nblocked_threads, "Specify amount of threads"),
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OPT_UINTEGER('w', "nwakers", &nwaking_threads, "Specify amount of waking threads"),
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OPT_BOOLEAN( 's', "silent", &silent, "Silent mode: do not display data/details"),
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OPT_BOOLEAN( 'S', "shared", &fshared, "Use shared futexes instead of private ones"),
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OPT_END()
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};
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static const char * const bench_futex_wake_parallel_usage[] = {
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"perf bench futex wake-parallel <options>",
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NULL
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};
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static void *waking_workerfn(void *arg)
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{
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struct thread_data *waker = (struct thread_data *) arg;
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struct timeval start, end;
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pthread_barrier_wait(&barrier);
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gettimeofday(&start, NULL);
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waker->nwoken = futex_wake(&futex, nwakes, futex_flag);
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if (waker->nwoken != nwakes)
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warnx("couldn't wakeup all tasks (%d/%d)",
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waker->nwoken, nwakes);
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gettimeofday(&end, NULL);
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timersub(&end, &start, &waker->runtime);
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pthread_exit(NULL);
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return NULL;
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}
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static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr)
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{
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unsigned int i;
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pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE);
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pthread_barrier_init(&barrier, NULL, nwaking_threads + 1);
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/* create and block all threads */
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for (i = 0; i < nwaking_threads; i++) {
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/*
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* Thread creation order will impact per-thread latency
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* as it will affect the order to acquire the hb spinlock.
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* For now let the scheduler decide.
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*/
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if (pthread_create(&td[i].worker, &thread_attr,
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waking_workerfn, (void *)&td[i]))
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err(EXIT_FAILURE, "pthread_create");
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}
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pthread_barrier_wait(&barrier);
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for (i = 0; i < nwaking_threads; i++)
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if (pthread_join(td[i].worker, NULL))
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err(EXIT_FAILURE, "pthread_join");
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pthread_barrier_destroy(&barrier);
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}
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static void *blocked_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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while (1) { /* handle spurious wakeups */
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if (futex_wait(&futex, 0, NULL, futex_flag) != EINTR)
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break;
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}
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pthread_exit(NULL);
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return NULL;
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}
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static void block_threads(pthread_t *w, pthread_attr_t thread_attr,
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struct cpu_map *cpu)
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{
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cpu_set_t cpuset;
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unsigned int i;
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threads_starting = nblocked_threads;
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/* create and block all threads */
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for (i = 0; i < nblocked_threads; i++) {
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CPU_ZERO(&cpuset);
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CPU_SET(cpu->map[i % cpu->nr], &cpuset);
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if (pthread_attr_setaffinity_np(&thread_attr, sizeof(cpu_set_t), &cpuset))
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err(EXIT_FAILURE, "pthread_attr_setaffinity_np");
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if (pthread_create(&w[i], &thread_attr, blocked_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 print_run(struct thread_data *waking_worker, unsigned int run_num)
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{
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unsigned int i, wakeup_avg;
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double waketime_avg, waketime_stddev;
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struct stats __waketime_stats, __wakeup_stats;
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init_stats(&__wakeup_stats);
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init_stats(&__waketime_stats);
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for (i = 0; i < nwaking_threads; i++) {
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update_stats(&__waketime_stats, waking_worker[i].runtime.tv_usec);
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update_stats(&__wakeup_stats, waking_worker[i].nwoken);
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}
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waketime_avg = avg_stats(&__waketime_stats);
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waketime_stddev = stddev_stats(&__waketime_stats);
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wakeup_avg = avg_stats(&__wakeup_stats);
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printf("[Run %d]: Avg per-thread latency (waking %d/%d threads) "
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"in %.4f ms (+-%.2f%%)\n", run_num + 1, wakeup_avg,
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nblocked_threads, waketime_avg / USEC_PER_MSEC,
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rel_stddev_stats(waketime_stddev, waketime_avg));
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}
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static void print_summary(void)
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{
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unsigned int wakeup_avg;
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double waketime_avg, waketime_stddev;
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waketime_avg = avg_stats(&waketime_stats);
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waketime_stddev = stddev_stats(&waketime_stats);
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wakeup_avg = avg_stats(&wakeup_stats);
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printf("Avg per-thread latency (waking %d/%d threads) in %.4f ms (+-%.2f%%)\n",
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wakeup_avg,
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nblocked_threads,
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waketime_avg / USEC_PER_MSEC,
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rel_stddev_stats(waketime_stddev, waketime_avg));
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}
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static void do_run_stats(struct thread_data *waking_worker)
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{
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unsigned int i;
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for (i = 0; i < nwaking_threads; i++) {
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update_stats(&waketime_stats, waking_worker[i].runtime.tv_usec);
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update_stats(&wakeup_stats, waking_worker[i].nwoken);
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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_parallel(int argc, const char **argv)
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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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struct thread_data *waking_worker;
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struct cpu_map *cpu;
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argc = parse_options(argc, argv, options,
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bench_futex_wake_parallel_usage, 0);
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if (argc) {
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usage_with_options(bench_futex_wake_parallel_usage, options);
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exit(EXIT_FAILURE);
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}
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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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cpu = cpu_map__new(NULL);
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if (!cpu)
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err(EXIT_FAILURE, "calloc");
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if (!nblocked_threads)
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nblocked_threads = cpu->nr;
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/* some sanity checks */
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if (nwaking_threads > nblocked_threads || !nwaking_threads)
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nwaking_threads = nblocked_threads;
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if (nblocked_threads % nwaking_threads)
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errx(EXIT_FAILURE, "Must be perfectly divisible");
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/*
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* Each thread will wakeup nwakes tasks in
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* a single futex_wait call.
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*/
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nwakes = nblocked_threads/nwaking_threads;
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blocked_worker = calloc(nblocked_threads, sizeof(*blocked_worker));
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if (!blocked_worker)
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err(EXIT_FAILURE, "calloc");
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if (!fshared)
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futex_flag = FUTEX_PRIVATE_FLAG;
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printf("Run summary [PID %d]: blocking on %d threads (at [%s] "
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"futex %p), %d threads waking up %d at a time.\n\n",
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getpid(), nblocked_threads, fshared ? "shared":"private",
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&futex, nwaking_threads, 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 < bench_repeat && !done; j++) {
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waking_worker = calloc(nwaking_threads, sizeof(*waking_worker));
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if (!waking_worker)
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err(EXIT_FAILURE, "calloc");
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/* create, launch & block all threads */
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block_threads(blocked_worker, thread_attr, cpu);
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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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wakeup_threads(waking_worker, thread_attr);
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for (i = 0; i < nblocked_threads; i++) {
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ret = pthread_join(blocked_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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do_run_stats(waking_worker);
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if (!silent)
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print_run(waking_worker, j);
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free(waking_worker);
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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(blocked_worker);
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return ret;
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}
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#endif /* HAVE_PTHREAD_BARRIER */
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