From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751312AbdK0EYm (ORCPT ); Sun, 26 Nov 2017 23:24:42 -0500 Received: from smtp2.provo.novell.com ([137.65.250.81]:34220 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751231AbdK0EYk (ORCPT ); Sun, 26 Nov 2017 23:24:40 -0500 From: Davidlohr Bueso To: acme@kernel.org Cc: james.yang@arm.com, kim.phillips@arm.com, dave@stgolabs.net, linux-kernel@vger.kernel.org, Kim Phillips Subject: [PATCH 3/3] perf bench futex: sync waker threads Date: Sun, 26 Nov 2017 20:21:01 -0800 Message-Id: <20171127042101.3659-4-dave@stgolabs.net> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20171127042101.3659-1-dave@stgolabs.net> References: <20171127042101.3659-1-dave@stgolabs.net> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: James Yang 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. Cc: Kim Phillips Signed-off-by: James Yang --- tools/perf/bench/futex-wake-parallel.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/tools/perf/bench/futex-wake-parallel.c b/tools/perf/bench/futex-wake-parallel.c index c04e207ea37c..55bff8673d31 100644 --- a/tools/perf/bench/futex-wake-parallel.c +++ b/tools/perf/bench/futex-wake-parallel.c @@ -43,6 +43,7 @@ static bool affine_wakers = false; static unsigned int nblocked_threads = 0, nwaking_threads = 0; static pthread_mutex_t thread_lock; static pthread_cond_t thread_parent, thread_worker; +static pthread_barrier_t barrier; static struct stats waketime_stats, wakeup_stats; static unsigned int threads_starting; static int futex_flag = 0; @@ -66,6 +67,8 @@ static void *waking_workerfn(void *arg) struct thread_data *waker = (struct thread_data *) arg; struct timeval start, end; + pthread_barrier_wait(&barrier); + gettimeofday(&start, NULL); waker->nwoken = futex_wake(&futex, nwakes, futex_flag); @@ -87,6 +90,8 @@ static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr, pthread_attr_setdetachstate(&thread_attr, PTHREAD_CREATE_JOINABLE); + pthread_barrier_init(&barrier, NULL, nwaking_threads + 1); + /* create and block all threads */ for (i = 0; i < nwaking_threads; i++) { /* @@ -110,9 +115,13 @@ static void wakeup_threads(struct thread_data *td, pthread_attr_t thread_attr, err(EXIT_FAILURE, "pthread_create"); } + pthread_barrier_wait(&barrier); + for (i = 0; i < nwaking_threads; i++) if (pthread_join(td[i].worker, NULL)) err(EXIT_FAILURE, "pthread_join"); + + pthread_barrier_destroy(&barrier); } static void *blocked_workerfn(void *arg __maybe_unused) -- 2.13.6