Re: [RFC] Performance monitoring units and KVM

[Balaji Rao <balajirrao@gmail.com>]

On Sunday 17 February 2008 03:34:43 am Anthony Liguori wrote:
> Balaji Rao wrote:
> > Hi all!
> >
> > Earlier it was suggested that we go ahead with emulating Perf Mon Events
> > in exposing it to the guest. The serious limitation in this approach is
> > that we end up exposing only a small number of events to the guest, even
> > though the host hardware is capable of much more. The only benefit this
> > approach offers is that, it doesn't break live migration.
>
> I think performance monitors are no different than anything else in
> KVM.  We should virtualize as much as possible and by default provide
> only the common subset to the guest supported by the majority of hardware.
>
> Then we can use mechanisms like QEMU's CPU support to enable additional
> features that may be available and unique to the underlying hardware.
> It's then up to the management tools to deal with migratability since
> they've explicitly enabled the feature.

Sorry, I don't understand how it can done through QEMU, but according to what I 
understand, it makes migration very difficult/impossible. So, why should we go 
for this approach at all ? Its the very reason direct access to PMU was thought 
of as a bad idea.

Do you see any other problem in directly exposing the PMU ?

-- 
regards,

balaji rao
NITK

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