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Date: Mon, 15 Jun 2009 12:18:12 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Avi Kivity <avi@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Ingo Molnar <mingo@elte.hu>, mingo@redhat.com, paulus@samba.org,
       acme@redhat.com, linux-kernel@vger.kernel.org, penberg@cs.helsinki.fi,
       vegard.nossum@gmail.com, efault@gmx.de, jeremy@goop.org,
       npiggin@suse.de, tglx@linutronix.de, linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support
 to use NMI-safe methods
References: <tip-74193ef0ecab92535c8517f082f1f50504526c9b@git.kernel.org>	 <alpine.LFD.2.01.0906151007560.3305@localhost.localdomain>	 <20090615171845.GA7664@elte.hu>	 <alpine.LFD.2.01.0906151029160.3305@localhost.localdomain>	 <4A369508.2090707@zytor.com> <20090615184858.GD6520@Krystal>	 <1245091917.6741.185.camel@laptop>  <20090615185907.GF6520@Krystal> <1245092561.6741.205.camel@laptop> <4A369E00.2090408@redhat.com>
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Avi Kivity wrote:
> 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.
> 

Sounds like a win to me.

	-hpa