Date: Thu, 26 Aug 2010 11:22:46 -0400
From: Don Zickus <dzickus@redhat.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Robert Richter <robert.richter@amd.com>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>, Lin Ming <ming.m.lin@intel.com>,
        "fweisbec@gmail.com" <fweisbec@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Huang, Ying" <ying.huang@intel.com>, Yinghai Lu <yinghai@kernel.org>,
        Andi Kleen <andi@firstfloor.org>
Subject: Re: [PATCH -v3] perf, x86: try to handle unknown nmis with running
 perfctrs
Message-ID: <20100826152246.GN4879@redhat.com>
References: <9g472epksbkxhgmw6a3qh8r5.1282316687153@email.android.com>
 <20100820152510.GA4167@elte.hu>
 <20100825094819.GB3198@erda.amd.com>
 <20100825104130.GA27891@elte.hu>
 <20100825110006.GB27891@elte.hu>
 <20100825201106.GH4879@redhat.com>
 <20100826090008.GA22783@erda.amd.com>
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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@amd.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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