Messages in this thread | | | Subject | Re: [RFC][PATCH 6/6] perf, tools: X86 RDPMC, RDTSC test | From | Peter Zijlstra <> | Date | Mon, 21 Nov 2011 16:37:22 +0100 |
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On Mon, 2011-11-21 at 16:29 +0100, Stephane Eranian wrote: > Peter, > > I don't see how this test and infrastructure handles the case where the event > is multiplexed. I know there is time_enabled and time_running. But those are > not sync'd to the moment of the rdpmc(). I think there needs to be some other > timestamp in the mmap struct so the user can compute a delta to then add to > time_enabled and time_running.
When the counter isn't actually on the PMU, ->index will be 0 and rdpmc should not be attempted.
> Unless, we assume the two time metrics are there ONLY to compute a scaling > ratio. In which case, I think, we don't need the delta because if we > can do rdpmc() > it means the event is currently scheduled and thus time_enabled and time_running > are both ticking which means the scaling ratio does not change since the moment > the event was scheduled in.
Right, you don't need delta to compute the scale, but its useful for user-space time based measurements, Arun wanted to do something like that.
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