From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758535Ab0ERRSS (ORCPT ); Tue, 18 May 2010 13:18:18 -0400 Received: from hera.kernel.org ([140.211.167.34]:60774 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932070Ab0ERRR4 (ORCPT ); Tue, 18 May 2010 13:17:56 -0400 Date: Tue, 18 May 2010 17:17:31 GMT From: tip-bot for Peter Zijlstra Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, mingo@elte.hu In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:perf/core] perf: Optimize perf_output_*() by avoiding local_xchg() Message-ID: Git-Commit-ID: 6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.3 (hera.kernel.org [127.0.0.1]); Tue, 18 May 2010 17:17:31 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 Gitweb: http://git.kernel.org/tip/6d1acfd5c6bfd5231c13a8f2858d7f2afbaa1b62 Author: Peter Zijlstra AuthorDate: Tue, 18 May 2010 11:12:48 +0200 Committer: Ingo Molnar CommitDate: Tue, 18 May 2010 18:35:49 +0200 perf: Optimize perf_output_*() by avoiding local_xchg() Since the x86 XCHG ins implies LOCK, avoid the use by using a sequence count instead. Signed-off-by: Peter Zijlstra LKML-Reference: Signed-off-by: Ingo Molnar --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index ce76676..fe50347 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -804,6 +804,7 @@ struct perf_output_handle { struct perf_mmap_data *data; unsigned long head; unsigned long offset; + unsigned long wakeup; int nmi; int sample; }; diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 1f98c78..7e3bcf1 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -2917,6 +2917,7 @@ static void perf_output_get_handle(struct perf_output_handle *handle) preempt_disable(); local_inc(&data->nest); + handle->wakeup = local_read(&data->wakeup); } static void perf_output_put_handle(struct perf_output_handle *handle) @@ -2950,7 +2951,7 @@ again: goto again; } - if (local_xchg(&data->wakeup, 0)) + if (handle->wakeup != local_read(&data->wakeup)) perf_output_wakeup(handle); preempt_enable();