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: <4C208B09.9030003@redhat.com>
Date:	Tue, 22 Jun 2010 13:06:01 +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 01:02 PM, Peter Zijlstra wrote:
> On Tue, 2010-06-22 at 12:53 +0300, Avi Kivity wrote:
>
>
>    
>>> /me has no clue what virtual MSRs are,
>>>        
>> MSRs that are not defined by the hardware, but instead by the
>> hypervisor.
>>
>>      
> Uhm, but the PMU MSRs are all defined by the hardware, if you move the
> PMU MSRs around nothing will work.. *confusion*
>    

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.

>> When emulating the hardware PMU we can be clever at times and allow
>> RDPMC not to trap.
>>      
> Sure, not disagreeing with that, still the generic case is to trap, so
> lets first get that to work and then try and be smart :-)
>    

That's what we're doing here.

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

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