linux-kernel - Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods

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Date:	Mon, 15 Jun 2009 22:21:35 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, paulus@...ba.org, acme@...hat.com,
	linux-kernel@...r.kernel.org, penberg@...helsinki.fi,
	vegard.nossum@...il.com, efault@....de, jeremy@...p.org,
	npiggin@...e.de, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support
 to use NMI-safe methods

On 06/15/2009 10:10 PM, Peter Zijlstra wrote:
>> But one thing is sure: it is certainly going to be faster than the
>> INVLPG(s!) we have to do with the GUP solution.
>>      
>
> Sure, but we only pay that price when we do the callchain bit, not on
> every NMI.
>    

You can read cr2 on nmi entry and nmi exit, and only write it if it has 
changed (if it turns out that writing cr2 is expensive; ISTR that it isn't).

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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