linux-kernel - Re: [PATCH v2] perf/x86/intel: ignore CondChgd bit to avoid false NMI handling

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Message-ID: <20140630222224.GH19781@tassilo.jf.intel.com>
Date:	Mon, 30 Jun 2014 15:22:24 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	"HATAYAMA, Daisuke" <d.hatayama@...fujitsu.com>
Cc:	hpa@...or.com, Don Zickus <dzickus@...hat.com>,
	matt@...sole-pimps.org, peterz@...radead.org, acme@...nel.org,
	mingo@...hat.com, paulus@...ba.org, tglx@...utronix.de,
	x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] perf/x86/intel: ignore CondChgd bit to avoid false
 NMI handling

> 
> I'm also interested in the behaviour of CondChgd bit on Ivy Bridge processors.

The intended meaning of CondChgd is that a hardware debugger has taken over the
PMU. It shouldn't really be set in other circumstances.

I think right now for perf it would be best to just ignore it.

In theory could stop using the PMU, but if some BIOS set it it would
completely disable perf there. So better to just ignore it.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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