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

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Date:	Tue, 7 Feb 2012 11:31:24 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, 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()

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.

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.
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