From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757628Ab0ERNq5 (ORCPT ); Tue, 18 May 2010 09:46:57 -0400 Received: from casper.infradead.org ([85.118.1.10]:54186 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757516Ab0ERNqp (ORCPT ); Tue, 18 May 2010 09:46:45 -0400 Message-Id: <20100518133726.128688672@chello.nl> User-Agent: quilt/0.48-1 Date: Tue, 18 May 2010 15:33:02 +0200 From: Peter Zijlstra To: Ingo Molnar , Paul Mackerras , Arnaldo Carvalho de Melo Cc: Frederic Weisbecker , Steven Rostedt , Thomas Gleixner , linux-kernel@vger.kernel.org, Peter Zijlstra Subject: [PATCH 4/5] perf: Avoid local_xchg References: <20100518133258.000434886@chello.nl> Content-Disposition: inline; filename=perf-buffer-no-xchg-wakeup.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since the x86 XCHG ins implies LOCK, avoid the use by using a sequence count instead. Signed-off-by: Peter Zijlstra --- include/linux/perf_event.h | 1 + kernel/perf_event.c | 3 ++- 2 files changed, 3 insertions(+), 1 deletion(-) Index: linux-2.6/include/linux/perf_event.h =================================================================== --- linux-2.6.orig/include/linux/perf_event.h +++ linux-2.6/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; }; Index: linux-2.6/kernel/perf_event.c =================================================================== --- linux-2.6.orig/kernel/perf_event.c +++ linux-2.6/kernel/perf_event.c @@ -2917,6 +2917,7 @@ static void perf_output_get_handle(struc 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();