linux-kernel - Re: [PATCH 5/5] perf, x86: Move NMI clearing to end of PMI handler after the counter registers are reset

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Date:	Wed, 13 Feb 2013 10:10:22 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, eranian@...gle.com,
	Andi Kleen <ak@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH 5/5] perf, x86: Move NMI clearing to end of PMI handler
 after the counter registers are reset


* Andi Kleen <andi@...stfloor.org> wrote:

> On Tue, Feb 12, 2013 at 09:43:46AM +0100, Ingo Molnar wrote:
> > Was this stress-tested on all affected main CPU types, or only 
> > on Haswell?
> 
> I tested it on Haswell and Ivy Bridge. I can also try Westmere 
> and a Saltwell(Atom), but for the majority of other family 6 
> systems I'll need to rely on the community.

The systems you tested should be OK.

> White listing is somewhat difficult because it affects the 
> architectural mode too.

Yeah, I'd rather avoid that.

> I don't really expect problems from this change, we should 
> probably have always done it like this.

I expect potential problems: the ordering of the operations in 
the NMI handler was always very fragile, resulting in hard to 
debug hangs - which sometimes needed hours long very intense PMU 
stress-testing to trigger.

That is why I asked how heavily you've tested this. Once the 
series passes review I'll keep this patch last to make it easy 
to revert/zap if it causes problems.

Thanks,

	Ingo
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