KVM PMU virtualization

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

Hi,

It looks like several of us have been looking at how to use the PMU
for virtualization. Rather than continuing to have discussions in
smaller groups, I think it is a good idea we move it to the mailing
lists to see what we can share and avoid duplicate efforts.

There are really two separate things to handle:

1) Add support to perf to allow it to monitor a KVM guest from the
    host.

2) Allow guests access to the PMU (or an emulated PMU), making it
    possible to run perf on applications running within the guest.

I know some of you have been looking at 1) and I am currently working
on 2). I have been looking at various approaches, including whether it
is feasible to share the PMU between the host and multiple guests. For
now I am going to focus on allowing one guest to take control of the
PMU, then later hopefully adding support for multiplexing it between
multiple guests.

Eventually we will see proper hardware PMU virtualization from Intel and
AMD (admittedly I have only looked at the Intel specs so far), and by
then be able to allow the host as well as the guests to share the PMU.

If anybody else is working on this, I'd love to hear about it so we can
coordinate our efforts. The main purpose with this mail was really to
being the discussion to the mailing list to avoid duplicated efforts.

Cheers,
Jes

PS: I'll be AFK all of next week, so it may take a few days for me to
reply to follow-up discussions.