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

[Avi Kivity <avi@redhat.com>]

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