linux-kernel - Re: [PATCH] perf: fix assertion failure in x86_pmu

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Message-ID: <20120207104952.GB4328@elte.hu>
Date:	Tue, 7 Feb 2012 11:49:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	markus@...ppelsdorf.de, paulus@...ba.org
Subject: Re: [PATCH] perf: fix assertion failure in x86_pmu_start()


* Stephane Eranian <eranian@...gle.com> wrote:

> On Tue, Feb 7, 2012 at 11:25 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Le mardi 07 février 2012 à 09:41 +0100, Ingo Molnar a écrit :
> >
> >> Were these messages introduced by:
> >>
> >>  e050e3f0a71b: perf: Fix broken interrupt rate throttling
> >>
> >> as well?
> >>
> >> In any case I'm holding off on applying the patch before this is
> >> resolved.
> >
> > Reverting e050e3f0a71b solves all my problems, no more warnings.
> >
> > $ perf record -a -g hackbench 10 thread 4000
> > Running with 10*40 (== 400) tasks.
> > Time: 13.181
> > [ perf record: Woken up 59 times to write data ]
> > [ perf record: Captured and wrote 16.874 MB perf.data (~737228 samples)
> > ]
> >
> > $ perf record -a -g hackbench 10 thread 4000
> > Running with 10*40 (== 400) tasks.
> > Time: 13.124
> > [ perf record: Woken up 61 times to write data ]
> > [ perf record: Captured and wrote 16.533 MB perf.data (~722349 samples)
> > ]
> >
>
> What system is this running on?
> The problem is that without e050e3f0a71b interrupt throttling does not work.

Fixes are not supposed to regress, so if we cannot resolve this 
within a couple of days we'll have to revert e050e3f0a71b and 
re-try it later.

> I think the key difference is that without the patch, 
> frequency adjustment happens with the PMU completely stopped 
> whereas with my patch it does not. I suspect this may be the 
> issue. I can rework the patch to disable the PMU completely 
> while retaining the same workflow.

Would be nice to try that.

Thanks,

	Ingo
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