Re: KVM PMU virtualization

Ingo Molnar
2010-02-26T10:47:15Z

* Joerg Roedel <joro@8bytes.org> wrote:

> On Fri, Feb 26, 2010 at 11:46:34AM +0200, Avi Kivity wrote:
> > On 02/26/2010 10:42 AM, Ingo Molnar wrote:
> >> Note that the 'soft PMU' still sucks from a design POV as there's no generic
> >> hw interface to the PMU. So there would have to be a 'soft AMD' and a 'soft
> >> Intel' PMU driver at minimum.
> >>
> >
> > Right, this will severely limit migration domains to hosts of the same
> > vendor and processor generation. There is a middle ground, though,
> > Intel has recently moved to define an "architectural pmu" which is not
> > model specific. I don't know if AMD adopted it. We could offer both
> > options - native host capabilities, with a loss of compatibility, and
> > the architectural pmu, with loss of model specific counters.
>
> I only had a quick look yet on the architectural pmu from intel but it looks
> like it can be emulated for a guest on amd using existing features.

AMD CPUs dont have enough events for that, they cannot do the 3 fixed events
in addition to the 2 generic ones.

Nor do you really want to standardize on KVM guests on returning
'GenuineIntel' in CPUID, so that the various guest side OSs use the Intel PMU
drivers, right?

Ingo