Re: KVM PMU virtualization

[Jes Sorensen <Jes.Sorensen@redhat.com>]

On 02/25/10 17:26, Ingo Molnar wrote:
>> Given that perf can apply the PMU to individual host tasks, I don't see
>> fundamental problems multiplexing it between individual guests (which can
>> then internally multiplex it again).
>
> In terms of how to expose it to guests, a 'soft PMU' might be a usable
> approach. Although to Linux guests you could expose much more functionality
> and an non-PMU-limited number of instrumentation events, via a more
> intelligent interface.
>
> But note that in terms of handling it on the host side the PMU approach is not
> acceptable: instead it should map to proper perf_events, not try to muck with
> the PMU itself.

I am not keen on emulating the PMU, if we do that we end up having to
emulate a large number of MSR accesses, which is really costly. It makes
a lot more sense to give the guest direct access to the PMU. The problem
here is how to manage it without too much overhead.

Cheers,
Jes