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

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Date:	Fri, 27 Aug 2010 10:31:20 +0200
From:	Robert Richter <robert.richter@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Cyrill Gorcunov <gorcunov@...il.com>,
	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	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 27.08.10 04:11:21, Peter Zijlstra wrote:
> On Fri, 2010-08-27 at 09:57 +0200, Robert Richter wrote:
> > On 26.08.10 14:02:50, Cyrill Gorcunov wrote:
> > > > diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> > > > index 4539b4b..9e65a7b 100644
> > > > --- a/arch/x86/kernel/cpu/perf_event_intel.c
> > > > +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> > > > @@ -777,7 +777,9 @@ again:
> > > >  
> > > >  done:
> > > >  	intel_pmu_enable_all(0);
> > > > -	return handled;
> > > > +	if (!handled)
> > > > +		return handled;
> > > > +	return ++handled;
> > > >  }
> > > >  
> > > >  static struct event_constraint *
> > > > 
> > > 
> > > ok, it seems it just treat any unknown nmi as being came from PMU, no?
> > 
> > Yes, this just throws away all unknown nmis after a perf nmi. It
> > disables unknown nmi detection on this cpu type.
> 
> Wouldn't returning 2 be more sensible, then it would only eat a few
> unknowns after each pmi? (Still assuming you return 0 when there really
> was nothing to do)

Yes, this would be the best workaround for cpus where the detection
logic does not work properly. But I think Don found a solution
already.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center

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