linux-kernel - Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running perfctrs

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Date:	Thu, 26 Aug 2010 11:22:46 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Lin Ming <ming.m.lin@...el.com>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running
 perfctrs

On Thu, Aug 26, 2010 at 01:18:29PM +0400, Cyrill Gorcunov wrote:
> On Thu, Aug 26, 2010 at 1:00 PM, Robert Richter <robert.richter@....com> wrote:
> ...
> >
> > This could also be a race in the counter handling code, or we do not
> > proper count the number of handled counters. Maybe 2 counters actually
> > fired but we only noticed one counter and then accidentially cleared
> > the 2nd without processing it.
> >
> > -Robert
> >
> 
> Any chance to get it tested on P4 machine since it has a bit
> different design?

Hmm, I take that back.  I guess I can reproduce this on my i5 that I had
using Ingo's config.

Working on Robert's assumption, I added code to perf_event_intel.c that
said if handled !=0 just add one to it (IOW always process handled as 0 or
 something >1).  That seems to working good and catches the nmis that Ingo
was seeing.

I'll keep looking for the race condition to better fix it.

Cheers,
Don
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