linux-kernel - Re: [PATCH V2 1/5] ara virt interface of perf to support kvm guest os statistics collection in guest os

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Message-ID: <4C2097F4.1080402@redhat.com>
Date:	Tue, 22 Jun 2010 14:01:08 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Jes Sorensen <Jes.Sorensen@...hat.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Fr??d??ric Weisbecker <fweisbec@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Lin Ming <ming.m.lin@...el.com>,
	Sheng Yang <sheng@...ux.intel.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>, Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, zhiteng.huang@...el.com,
	tim.c.chen@...el.com
Subject: Re: [PATCH V2 1/5] ara virt interface of perf to support kvm guest
 os statistics collection in guest os

On 06/22/2010 01:10 PM, Peter Zijlstra wrote:
> On Tue, 2010-06-22 at 13:06 +0300, Avi Kivity wrote:
>
>    
>> You have a set of MSRs for real hardware (actually several sets)
>> discoverable by cpuid bits.  You have another set of MSRs, using other
>> indexes, discoverable by more CPUID bits.
>>
>> The new MSR indexes will always #GP on real hardware, but will be
>> trapped and serviced by kvm.  In effect kvm will pretend to have a
>> hardware-like PMU but done according to its own specifications.
>>      
> So what's the point?

We already have infrastructure for save/restore around MSRs.  They are 
state-based (as opposed to function-based hypercalls), so it's easy to 
live migrate by copying the MSR values.

> I thought the whole MSR interface thing was purely
> to let other-o$ play with the PMU, but if you move it around like that
> and make it KVM specific, nobody will find it...
>    

Other-os support will be achieved by emulating an existing interface.

-- 
error compiling committee.c: too many arguments to function

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