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SubjectRe: 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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