On Tue, 08 Jan 2019 11:25:13 +0000,
Andrew Murray <andrew.mur...@arm.com> wrote:
Hi Andrew,
> My only doubt about this is as follows. If, on a KVM host you run this:
>
> perf stat -e cycles:H lkvm run ...
>
> then on the VHE host the cycles reported represents the entire non-guest
> cycles
> associated with running the guest.
>
> On a !VHE, the cycles reported exclude EL2 (with or without this patch) and
> thus you don't get a representation of all the non-guest cycles associated
> with
> the guest. However without this patch you could at least still run:
>
> perf stat -e cycles:H -e cycles:h lkvm run ...
>
> and then add the two cycle counts together to get something comparative with
> the VHE host.
>
> If the above patch represents the desired semantics, then perhaps we must
> count
> both EL1 and *EL2* for !exclude_kernel on !VHE. In fact I think we should do
> this anyway and remove a little complexity from armv8pmu_set_event_filter.
> Thoughts?
I'm not sure we should hide the architectural differences between VHE
and !VHE. If you're trying to measure what is happening at in the
hypervisor, you can't reason about it while ignoring the dual nature
of !VHE.
Thanks,
M.
--
Jazz is not dead, it just smell funny.
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