Re: KVM PMU virtualization

Ingo Molnar
2010-02-26T13:32:22Z

* Avi Kivity <avi@redhat.com> wrote:

> Or do you mean to define a new, kvm-specific pmu model and feed it off the
> host pmu? In this case all the guests will need to be taught about it,
> which raises the compatibility problem.

You are missing two big things wrt. compatibility here:

1) The first upgrade overhead a one time overhead only.

2) Once a Linux guest has upgraded, it will work in the future, with _any_
future CPU - _without_ having to upgrade the guest!

Dont you see the advantage of that? You can instrument an old system on new
hardware, without having to upgrade that guest for the new CPU support.

With the 'steal the PMU' messy approach the guest OS has to be upgraded to the
new CPU type all the time. Ad infinitum.

Ingo