Messages in this thread |  | | Date | Fri, 10 Oct 2014 13:02:02 +0100 | From | Matt Fleming <> | Subject | Re: [PATCH 10/11] perf/x86/intel: Support task events with Intel CQM |
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On Wed, 08 Oct, at 04:49:57PM, Peter Zijlstra wrote: > > The thing is, with multiplexing you cannot fail at event creation time > anyhow. The only time where you can 'fail' is when programming the PMU, > when its full its full. > > Those that don't fit, get to wait their turn.
For CQM it's not about "fitting" everything in the PMU but more about monitoring the same thing (task, cgroup) with different events, i.e. one thing with two RMIDs. We have the RMID recycling algorithm to make things fit, but that doesn't help us out here.
An example scenario that isn't supported by this patch series is monitoring a cgroup while simultaneously monitoring a task that's part of that cgroup. Whichever event is created second will fail at event init time.
And that seemed like a fair approach to me. But the more I think about it, the more I begin to agree that maybe we should allow users the flexibility to create conflicting events, particularly because there appears to be precedent in other parts of perf.
Hmm... "rotation" is starting to become my least favourite word.
-- Matt Fleming, Intel Open Source Technology Center
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