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

[Ingo Molnar <mingo@elte.hu>]

* Avi Kivity <avi@redhat.com> 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 
upstream?

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.

Thanks,

	Ingo