Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758528Ab2JXMOx (ORCPT ); Wed, 24 Oct 2012 08:14:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:63414 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758022Ab2JXMOw (ORCPT ); Wed, 24 Oct 2012 08:14:52 -0400 Date: Wed, 24 Oct 2012 14:14:07 +0200 From: Jiri Olsa To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , Ingo Molnar , Paul Mackerras , Corey Ashford , Frederic Weisbecker , Namhyung Kim Subject: Re: [PATCH 02/11] perf: Do not get values from disabled counters in group format read Message-ID: <20121024121406.GA5582@krava.brq.redhat.com> References: <1350743599-4805-1-git-send-email-jolsa@redhat.com> <1350743599-4805-3-git-send-email-jolsa@redhat.com> <1351008789.13456.37.camel@twins> <20121023165040.GA7553@krava.brq.redhat.com> <1351080078.13456.60.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1351080078.13456.60.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1898 Lines: 45 On Wed, Oct 24, 2012 at 02:01:18PM +0200, Peter Zijlstra wrote: > On Tue, 2012-10-23 at 18:50 +0200, Jiri Olsa wrote: > > On Tue, Oct 23, 2012 at 06:13:09PM +0200, Peter Zijlstra wrote: > > > On Sat, 2012-10-20 at 16:33 +0200, Jiri Olsa wrote: > > > > It's possible some of the counters in the group could be > > > > disabled when sampling member of the event group is reading > > > > the rest via PERF_SAMPLE_READ sample type processing. Disabled > > > > counters could then produce wrong numbers. > > > > > > > > Fixing that by reading only enabled counters for PERF_SAMPLE_READ > > > > sample type processing. > > > > > > > > > > However did you run into this? > > > > yep, with perf record -a > > > > hm, I just checked and we enable/disable event groups atomicaly.. > > I haven't checked that before because it seemed obvious :-/ > > > > So, I'm not sure now about the exact code path that triggered it > > in my test.. however you could always disable child event from > > group and hit this issue, but thats not what happened in perf. > > > > might be some other bug... I'll check > > Right, so I don't object to the patch per-se, I was just curious how you > ran into it, because ISTR what you just said, we enable all this stuff > together. > > Also, why would disabled counters give strange values? They'd simply > return the same old value time after time, right? well, x86_pmu_read calls x86_perf_event_update, which expects the event is active.. if it's not it'll update the count from whatever left in event.hw.idx counter.. could be uninitialized or used by others.. I can easily reproduce this one, so let's see.. ;) jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/