From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964949AbcJ1Rnn (ORCPT ); Fri, 28 Oct 2016 13:43:43 -0400 Received: from terminus.zytor.com ([198.137.202.10]:32772 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756456AbcJ1Rnk (ORCPT ); Fri, 28 Oct 2016 13:43:40 -0400 Date: Fri, 28 Oct 2016 10:43:09 -0700 From: tip-bot for Davidlohr Bueso Message-ID: Cc: linux-kernel@vger.kernel.org, dbueso@suse.de, tglx@linutronix.de, bigeasy@linutronix.de, dave@stgolabs.net, mingo@kernel.org, acme@redhat.com, hpa@zytor.com Reply-To: tglx@linutronix.de, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, dbueso@suse.de, hpa@zytor.com, dave@stgolabs.net, mingo@kernel.org, acme@redhat.com In-Reply-To: <1477342613-9938-2-git-send-email-dave@stgolabs.net> References: <1477342613-9938-2-git-send-email-dave@stgolabs.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf bench futex: Avoid worker cacheline bouncing Git-Commit-ID: e2e1680fda1573ebfdd6bba5d58f978044746993 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: e2e1680fda1573ebfdd6bba5d58f978044746993 Gitweb: http://git.kernel.org/tip/e2e1680fda1573ebfdd6bba5d58f978044746993 Author: Davidlohr Bueso AuthorDate: Mon, 24 Oct 2016 13:56:52 -0700 Committer: Arnaldo Carvalho de Melo CommitDate: Tue, 25 Oct 2016 09:50:47 -0300 perf bench futex: Avoid worker cacheline bouncing Sebastian noted that overhead for worker thread ops (throughput) accounting was producing 'perf' to appear in the profiles, consuming a non-trivial (i.e. 13%) amount of CPU. This is due to cacheline bouncing due to the increment of w->ops. We can easily fix this by just working on a local copy and updating the actual worker once done running, and ready to show the program summary. There is no danger of the worker being concurrent, so we can trust that no stale value is being seen by another thread. This also gets rid of the unnecessary cache alignment hack; its not worth it. Reported-by: Sebastian Andrzej Siewior Signed-off-by: Davidlohr Bueso Acked-by: Sebastian Andrzej Siewior Link: http://lkml.kernel.org/r/1477342613-9938-2-git-send-email-dave@stgolabs.net Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/bench/futex-hash.c | 11 +++++------ tools/perf/bench/futex-lock-pi.c | 4 +++- 2 files changed, 8 insertions(+), 7 deletions(-) diff --git a/tools/perf/bench/futex-hash.c b/tools/perf/bench/futex-hash.c index d9e5e80..da04b8c 100644 --- a/tools/perf/bench/futex-hash.c +++ b/tools/perf/bench/futex-hash.c @@ -39,15 +39,12 @@ static unsigned int threads_starting; static struct stats throughput_stats; static pthread_cond_t thread_parent, thread_worker; -#define SMP_CACHE_BYTES 256 -#define __cacheline_aligned __attribute__ ((aligned (SMP_CACHE_BYTES))) - struct worker { int tid; u_int32_t *futex; pthread_t thread; unsigned long ops; -} __cacheline_aligned; +}; static const struct option options[] = { OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"), @@ -66,8 +63,9 @@ static const char * const bench_futex_hash_usage[] = { static void *workerfn(void *arg) { int ret; - unsigned int i; struct worker *w = (struct worker *) arg; + unsigned int i; + unsigned long ops = w->ops; /* avoid cacheline bouncing */ pthread_mutex_lock(&thread_lock); threads_starting--; @@ -77,7 +75,7 @@ static void *workerfn(void *arg) pthread_mutex_unlock(&thread_lock); do { - for (i = 0; i < nfutexes; i++, w->ops++) { + for (i = 0; i < nfutexes; i++, ops++) { /* * We want the futex calls to fail in order to stress * the hashing of uaddr and not measure other steps, @@ -91,6 +89,7 @@ static void *workerfn(void *arg) } } while (!done); + w->ops = ops; return NULL; } diff --git a/tools/perf/bench/futex-lock-pi.c b/tools/perf/bench/futex-lock-pi.c index 936d89d..7032e46 100644 --- a/tools/perf/bench/futex-lock-pi.c +++ b/tools/perf/bench/futex-lock-pi.c @@ -75,6 +75,7 @@ static void toggle_done(int sig __maybe_unused, static void *workerfn(void *arg) { struct worker *w = (struct worker *) arg; + unsigned long ops = w->ops; pthread_mutex_lock(&thread_lock); threads_starting--; @@ -103,9 +104,10 @@ static void *workerfn(void *arg) if (ret && !silent) warn("thread %d: Could not unlock pi-lock for %p (%d)", w->tid, w->futex, ret); - w->ops++; /* account for thread's share of work */ + ops++; /* account for thread's share of work */ } while (!done); + w->ops = ops; return NULL; }