linux-kernel - Re: perf: WARNING perfevents: irq loop stuck!

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Date:	Fri, 8 May 2015 00:22:07 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: perf: WARNING perfevents: irq loop stuck!

On Fri, 1 May 2015, Ingo Molnar wrote:

> So 0000fffffffffffe corresponds to 2 events left until overflow, 
> right? And on Haswell we don't set x86_pmu.limit_period AFAICS, so we 
> allow these super short periods.
> 
> Maybe like on Broadwell we need a quirk on Nehalem/Haswell as well, 
> one similar to bdw_limit_period()? Something like the patch below?
> 
> Totally untested and such. I picked 128 because of Broadwell, but 
> lower values might work as well. You could try to increase it to 3 and 
> upwards and see which one stops triggering stuck NMI loops?

I spent a lot of time trying to come up with a test case that triggered 
this more reliably but failed.

It definitely is an issue with PMC0 being -2 causing the PMC0 bit in the 
status register getting stuck and no clearing.  Often there is also a PEBS 
event active at the same time but that might be coincidence.

With your patch applied I can't trigger the issue. I haven't tried 
narrowing down the exact value yet.

Vince
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