From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754380AbbJUJMz (ORCPT ); Wed, 21 Oct 2015 05:12:55 -0400 Received: from casper.infradead.org ([85.118.1.10]:50205 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754122AbbJUJMw (ORCPT ); Wed, 21 Oct 2015 05:12:52 -0400 Date: Wed, 21 Oct 2015 11:12:54 +0200 From: Peter Zijlstra To: Alexei Starovoitov Cc: Kaixu Xia , davem@davemloft.net, acme@kernel.org, mingo@redhat.com, masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, daniel@iogearbox.net, wangnan0@huawei.com, linux-kernel@vger.kernel.org, pi3orama@163.com, hekuang@huawei.com, netdev@vger.kernel.org Subject: Re: [PATCH V5 1/1] bpf: control events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Message-ID: <20151021091254.GF2881@worktop.programming.kicks-ass.net> References: <1445325735-121694-1-git-send-email-xiakaixu@huawei.com> <1445325735-121694-2-git-send-email-xiakaixu@huawei.com> <5626C5CE.8080809@plumgrid.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5626C5CE.8080809@plumgrid.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 20, 2015 at 03:53:02PM -0700, Alexei Starovoitov wrote: > On 10/20/15 12:22 AM, Kaixu Xia wrote: > >diff --git a/kernel/events/core.c b/kernel/events/core.c > >index b11756f..5219635 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 (unlikely(!atomic_read(&event->soft_enable))) > >+ return 0; > >+ > > if (event->overflow_handler) > > event->overflow_handler(event, data, regs); > > else > > Peter, > does this part look right or it should be moved right after > if (unlikely(!is_sampling_event(event))) > return 0; > or even to other function? > > It feels to me that it should be moved, since we probably don't > want to active throttling, period adjust and event_limit for events > that are in soft_disabled state. Depends on what its meant to do. As long as you let the interrupt happen, I think we should in fact do those things (maybe not the event_limit), but period adjustment and esp. throttling are important when the event is enabled. If you want to actually disable the event: pmu->stop() will make it stop, and you can restart using pmu->start(). And I suppose you can wrap that with a counter if you need nesting. I'm not sure if any of that is a viable solution, because the patch description is somewhat short on the problem statement. As is, I'm not too charmed with the patch, but lacking a better understanding of what exactly we're trying to achieve I'm struggling with proposing alternatives.