Messages in this thread | | | Date | Sun, 16 Feb 2014 20:43:30 +0100 | From | Andi Kleen <> | Subject | Re: [PATCH] perf, nmi: fix unknown NMI warning |
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The best APIC documentation are the old data sheets for the external APIC chips. I don't know if they cover things in such detail.
> In this case the latter NMI will actually have an overflow state to > process so it's not a spurious NMI.
But we cannot distinguish it right? The spurious detector would trigger in any case.
> > > And if we're in a state that PMIs get re-raised quickly, we should either > > regulate the period down or start throttling. > > It could be a different counter; where both run at 'normal' periods but > just near miss each other by accident.
That's true.
It would be only a problem if they somehow become synchronized that this happens very commonly. The usual defense against things like that is to add a little randomization (I remember Stephane had a patch for that some time ago). Also I believe it helps to have the periods be prime numbers. But right now don't have any evidence it's a real problem. I presume there's enough noise on a typical setup that any such states disappear again quickly enough.
-Andi
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