Re: [PATCH v1 5/5] KVM: Expose a version 1 architectural PMU toguests

From: Ingo Molnar
Date: Tue May 17 2011 - 15:41:33 EST

* Avi Kivity <avi@xxxxxxxxxx> wrote:

> Caveats:
> - counters that have PMI (interrupt) enabled stop counting after the
> interrupt is signalled. This is because we need one-shot samples
> that keep counting, which perf doesn't support yet

Hm, do you need more than perf_event::event_limit, or something special?

> - some combinations of INV and CMASK are not supported

Could you please describe this better, where does this limit come from?
If perf then this needs fixing.

> - counters keep on counting in the host as well as the guest

I suspect fixing this either needs a hw filter feature, or the ability to
disable/enable these events across VM exits/entries.

I would imagine the disable/enable to be rather expensive so hw help would be
preferred ...

I didnt see anything objectionable in your patches, but i'd like to have
Peter's Acked-by as well before we go forward. I think that in the long run
having a virtio-perf gateway would allow us a lot more tricks than just
arch-perfmon emulation:

- we could do things like propagate guest side traces over to the host

- we could control from the host which events we measure on the guest side

- etc.

How would you like to handle the flow of patches - should we merge #1,#2,#3 in
perf/core and you'd then merge #4,#5 via the KVM tree once the first bits hit

We could also set up a separate branch for these three commits, which you could
pull - this would allow all this to still hit .40.


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