linux-kernel - Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side

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Message-ID: <4BC6EDFF.3000702@redhat.com>
Date:	Thu, 15 Apr 2010 13:44:15 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Joerg Roedel <joro@...tes.org>
CC:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, zhiteng.huang@...el.com,
	tim.c.chen@...el.com, Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os	statistics
 from host side

On 04/15/2010 01:40 PM, Joerg Roedel wrote:
>
>> That means an NMI that happens outside guest code (for example, in the
>> mmu, or during the exit itself) would be counted as if in guest code.
>>      
> Hmm, true. The same is true for an NMI that happens between VMSAVE and
> STGI but that window is smaller. Anyway, I think we don't need the
> busy-wait loop. The NMI should be executed at a well defined point and
> we set the cpu_var back to NULL after that point.
>    

The point is not well defined.  Considering there are already at least 
two implementations svm, I don't want to rely on implementation details.

We could tune the position of the loop so that zero iterations are 
executed on the implementations we know about.

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

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