From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752130AbbJLMMa (ORCPT ); Mon, 12 Oct 2015 08:12:30 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:53851 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751173AbbJLMM3 (ORCPT ); Mon, 12 Oct 2015 08:12:29 -0400 Date: Mon, 12 Oct 2015 14:12:13 +0200 From: Peter Zijlstra To: "Wangnan (F)" Cc: Kaixu Xia , ast@plumgrid.com, davem@davemloft.net, acme@kernel.org, mingo@redhat.com, masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, daniel@iogearbox.net, linux-kernel@vger.kernel.org, pi3orama@163.com, hekuang@huawei.com, netdev@vger.kernel.org Subject: Re: [RFC PATCH 1/2] perf: Add the flag sample_disable not to output data on samples Message-ID: <20151012121213.GL17308@twins.programming.kicks-ass.net> References: <1444640563-159175-1-git-send-email-xiakaixu@huawei.com> <1444640563-159175-2-git-send-email-xiakaixu@huawei.com> <20151012120257.GO3816@twins.programming.kicks-ass.net> <561BA200.20108@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <561BA200.20108@huawei.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 12, 2015 at 08:05:20PM +0800, Wangnan (F) wrote: > > > On 2015/10/12 20:02, Peter Zijlstra wrote: > >On Mon, Oct 12, 2015 at 09:02:42AM +0000, Kaixu Xia wrote: > >>--- a/include/linux/perf_event.h > >>+++ b/include/linux/perf_event.h > >>@@ -483,6 +483,8 @@ struct perf_event { > >> perf_overflow_handler_t overflow_handler; > >> void *overflow_handler_context; > >>+ atomic_t *sample_disable; > >>+ > >> #ifdef CONFIG_EVENT_TRACING > >> struct trace_event_call *tp_event; > >> struct event_filter *filter; > >>diff --git a/kernel/events/core.c b/kernel/events/core.c > >>index b11756f..f6ef45c 100644 > >>--- a/kernel/events/core.c > >>+++ b/kernel/events/core.c > >>@@ -6337,6 +6337,9 @@ static int __perf_event_overflow(struct perf_event *event, > >> irq_work_queue(&event->pending); > >> } > >>+ if ((event->sample_disable) && atomic_read(event->sample_disable)) > >>+ return ret; > >>+ > >> if (event->overflow_handler) > >> event->overflow_handler(event, data, regs); > >> else > >Try and guarantee sample_disable lives in the same cacheline as > >overflow_handler. > > Could you please explain why we need them to be in a same cacheline? Because otherwise you've just added a cacheline miss to this relatively hot path.