From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH V2 1/5] ara virt interface of perf to support kvm guest
 os statistics collection in guest os
Date: Tue, 22 Jun 2010 14:01:08 +0300
Message-ID: <4C2097F4.1080402@redhat.com>
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Cc: Jes Sorensen <Jes.Sorensen@redhat.com>,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org,
	Ingo Molnar <mingo@elte.hu>,
	Fr??d??ric Weisbecker <fweisbec@gmail.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Lin Ming <ming.m.lin@intel.com>,
	Sheng Yang <sheng@linux.intel.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	oerg Roedel <joro@8bytes.org>, Gleb Natapov <gleb@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>, zhiteng.huang@intel.com,
	tim.c.chen@intel.com
To: Peter Zijlstra <peterz@infradead.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <1277201428.1875.696.camel@laptop>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

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