Re: KVM PMU virtualization

Zhang, Yanmin
2010-02-26T02:52:59Z

On Thu, 2010-02-25 at 18:34 +0100, Joerg Roedel wrote:
> On Thu, Feb 25, 2010 at 04:04:28PM +0100, Jes Sorensen wrote:
>
> > 1) Add support to perf to allow it to monitor a KVM guest from the
> > host.
>
> This shouldn't be a big problem. The PMU of AMD Fam10 processors can be
> configured to count only when in guest mode. Perf needs to be aware of
> that and fetch the rip from a different place when monitoring a guest.
The idea is we want to measure both host and guest at the same time, and
compare all the hot functions fairly.

>
> > 2) Allow guests access to the PMU (or an emulated PMU), making it
> > possible to run perf on applications running within the guest.
>
> The biggest problem I see here is teaching the guest about the available
> events. The available event sets are dependent on the processor family
> (at least on AMD).
> A simple approach would be shadowing the perf msrs which is a simple
> thing to do. More problematic is the reinjection of performance
> interrupts and performance nmis.
>
> I personally don't like a self-defined event-set as the only solution
> because that would probably only work with linux and perf. I think we
> should have a way (additionally to a soft-event interface) which allows
> to expose the host pmu events to the guest.
>
> Joerg
>