From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756540Ab0CKIfg (ORCPT ); Thu, 11 Mar 2010 03:35:36 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:57593 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753469Ab0CKIff convert rfc822-to-8bit (ORCPT ); Thu, 11 Mar 2010 03:35:35 -0500 Subject: Re: [PATCH] perf_events: improve task_sched_in() From: Peter Zijlstra To: eranian@google.com Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org, fweisbec@gmail.com, robert.richter@amd.com, davem@davemloft.net, perfmon2-devel@lists.sf.net In-Reply-To: <1268288765-5326-1-git-send-email-eranian@google.com> References: <1268288765-5326-1-git-send-email-eranian@google.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 11 Mar 2010 09:35:16 +0100 Message-ID: <1268296516.5279.912.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-03-10 at 22:26 -0800, eranian@google.com wrote: > This patch is an optimization in perf_event_task_sched_in() to avoid scheduling > the events twice in a row. Without it, the perf_disable()/perf_enable() pair > is invoked twice, thereby pinned events counts while scheduling flexible events > and we go throuh hw_perf_enable() twice. By encapsulating, the whole sequence > into perf_disable()/perf_enable() we ensure, hw_perf_enable() is going to be > invoked only once because of the refcount protection. Agreed, this makes perfect sense. Acked-by: Peter Zijlstra > Signed-off-by: Stephane Eranian > -- > perf_event.c | 4 ++++ > 1 file changed, 4 insertions(+) > > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -1382,6 +1382,8 @@ void perf_event_task_sched_in(struct task_struct *task) > if (cpuctx->task_ctx == ctx) > return; > > + perf_disable(); > + > /* > * We want to keep the following priority order: > * cpu pinned (that don't need to move), task pinned, > @@ -1394,6 +1396,8 @@ void perf_event_task_sched_in(struct task_struct *task) > ctx_sched_in(ctx, cpuctx, EVENT_FLEXIBLE); > > cpuctx->task_ctx = ctx; > + > + perf_enable(); > } > > #define MAX_INTERRUPTS (~0ULL)