linux-kernel - Re: [PATCH 4/7] perf, x86: Implement IBS interrupt handler

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Date:	Mon, 1 Aug 2011 12:38:23 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] perf, x86: Implement IBS interrupt handler

On Mon, Aug 01, 2011 at 05:21:43PM +0200, Peter Zijlstra wrote:
> On Mon, 2011-08-01 at 07:32 +0200, Robert Richter wrote:
> > > So IBS cannot trigger the whole unknown NMI business? Wouldn't ibs_op
> > > triggering while ibs_fetch just started latch the NMI line, the
> > > in-progress NMI would handle both, and we then end up with a spare NMI?
> > 
> > Ok, I will run some excessive testing of this. If this turns out to be
> > a problem I will change the code. Could this be on top of this patch
> > set then? 
> 
> Sure, if you somehow end up duplicating some logic I think you know
> about this common.c file you proposed ;-)
> 
> I kinda lost the current state of affairs wrt spurious NMIs, I think
> there's still a few reports out there. I recently read through some
> Intel errata and found the Intel PMU can send double PMIs under some
> circumstances (just to keep life interesting).

I tried looking into but everytime I applied workarounds for Intel errata
I wound up with more unknown NMIs and proving that a couple of them worked
(with trace_printks) seemed elusive.  I got frustrated and left it alone.

But yeah, Intel's perf has so many errata that I think if you kick the
box while running perf you can generate an unknown NMI.

> 
> I also haven't checked up on what the perf_event_nmi_handler() magic
> looks today, so I can't say if its a problem or not, but I thought I'd
> just mention it.

It hasn't changed much since Robert added his magic which handles the
majority of use cases for now.

Cheers,
Don
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