On 02/25/10 17:26, Ingo Molnar wrote:
Given that perf can apply the PMU to individual host tasks, I don't see
fundamental problems multiplexing it between individual guests (which can
then internally multiplex it again).
In terms of how to expose it to guests, a 'soft PMU' might be a usable
approach. Although to Linux guests you could expose much more functionality
and an non-PMU-limited number of instrumentation events, via a more
intelligent interface.
But note that in terms of handling it on the host side the PMU approach is not
acceptable: instead it should map to proper perf_events, not try to muck with
the PMU itself.
I am not keen on emulating the PMU, if we do that we end up having to
emulate a large number of MSR accesses, which is really costly. It makes
a lot more sense to give the guest direct access to the PMU. The problem
here is how to manage it without too much overhead.
Cheers,
Jes
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