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 22:16:16 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, 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 10:02 PM, Peter Zijlstra wrote:
> Ah, well, I have no idea who expensive cr2 is, if its like a regular
> register then it should be fine. If however its tons more expensive then
> we should really avoid it.
>
>    

IIRC it's pretty cheap, I measured it once when tuning the kvm context 
switch code.  I don't recall the exact numbers.

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

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