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

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Date:	Wed, 02 Jul 2014 10:07:14 +0900 (JST)
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	ak@...ux.intel.com
Cc:	hpa@...or.com, 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

From: Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v2] perf/x86/intel: ignore CondChgd bit to avoid false NMI handling
Date: Mon, 30 Jun 2014 15:22:24 -0700

>> 
>> 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.
> 

Thanks for your explanation.

The hardware debugger you mean is a kind of ITP?

> 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.
> 

I'll reflect this information in the patch description.

--
Thanks.
HATAYAMA, Daisuke

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