From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Jiri Olsa <jolsa@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
Ingo Molnar <mingo@elte.hu>, Paul Mackerras <paulus@samba.org>,
Corey Ashford <cjashfor@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Namhyung Kim <namhyung@kernel.org>
Subject: Re: [PATCH 02/11] perf: Do not get values from disabled counters in group format read
Date: Wed, 24 Oct 2012 14:01:18 +0200 [thread overview]
Message-ID: <1351080078.13456.60.camel@twins> (raw)
In-Reply-To: <20121023165040.GA7553@krava.brq.redhat.com>
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?
next prev parent reply other threads:[~2012-10-24 12:01 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-20 14:33 [PATCH 00/11] perf tool: Add PERF_SAMPLE_READ sample read support Jiri Olsa
2012-10-20 14:33 ` [PATCH 01/11] perf: Add PERF_EVENT_IOC_ID ioctl to return event ID Jiri Olsa
2012-10-20 14:33 ` [PATCH 02/11] perf: Do not get values from disabled counters in group format read Jiri Olsa
2012-10-23 16:13 ` Peter Zijlstra
2012-10-23 16:50 ` Jiri Olsa
2012-10-24 12:01 ` Peter Zijlstra [this message]
2012-10-24 12:14 ` Jiri Olsa
2012-10-24 12:32 ` Peter Zijlstra
2012-10-24 16:03 ` Jiri Olsa
2012-10-20 14:33 ` [PATCH 03/11] perf tool: Use PERF_EVENT_IOC_ID perf ioctl to read event id Jiri Olsa
2012-10-22 7:57 ` Namhyung Kim
2012-10-22 8:40 ` Jiri Olsa
2012-10-20 14:33 ` [PATCH 04/11] perf tool: Add support for parsing PERF_SAMPLE_READ sample type Jiri Olsa
2012-10-22 8:56 ` Namhyung Kim
2012-10-20 14:33 ` [PATCH 05/11] perf tool: Fix event ID retrieval for group format read case Jiri Olsa
2012-10-20 14:33 ` [PATCH 06/11] perf tool: Add perf_evlist__id2sid function to get event ID related data Jiri Olsa
2012-10-20 14:33 ` [PATCH 07/11] perf tool: Add PERF_SAMPLE_READ sample related processing Jiri Olsa
2012-10-20 14:33 ` [PATCH 08/11] perf tool: Add 'S' event/group modifier to read sample value Jiri Olsa
2012-10-20 14:33 ` [PATCH 09/11] perf test: Add parse events tests for leader sampling Jiri Olsa
2012-10-22 8:58 ` Namhyung Kim
2012-10-22 9:12 ` Jiri Olsa
2012-10-20 14:33 ` [PATCH 10/11] perf tool: Display period values for all group members Jiri Olsa
2012-10-20 14:33 ` [PATCH 11/11] perf record: Fix mmap error output condition Jiri Olsa
2012-10-30 12:11 ` [tip:perf/core] " tip-bot for Jiri Olsa
2012-10-21 16:38 ` [PATCH 00/11] perf tool: Add PERF_SAMPLE_READ sample read support Ingo Molnar
2012-10-22 8:09 ` Jiri Olsa
2012-10-22 8:51 ` Namhyung Kim
2012-10-22 9:15 ` Jiri Olsa
2012-10-22 7:32 ` Namhyung Kim
2012-10-22 7:53 ` Jiri Olsa
2012-10-22 8:53 ` Namhyung Kim
2012-10-22 9:06 ` Jiri Olsa
2012-10-26 1:29 ` Namhyung Kim
2012-10-26 9:14 ` Peter Zijlstra
2012-10-26 10:23 ` Jiri Olsa
2012-10-26 15:39 ` Namhyung Kim
2012-10-26 16:14 ` David Ahern
2012-10-26 16:25 ` Namhyung Kim
2012-10-26 16:47 ` David Ahern
2012-10-26 17:00 ` Arnaldo Carvalho de Melo
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