Re: [PATCH 10/11] perf/x86/intel: Support task events with Intel CQM

[Peter Zijlstra]

On Fri, Oct 10, 2014 at 01:02:02PM +0100, Matt Fleming wrote:
> 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.

That was what I had that conflict thing for, ISTR seeing some parts of
that here.

> 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.

Yeah, although typically its not this hard. CQM is 'interesting' because
its so different.

> Hmm... "rotation" is starting to become my least favourite word.

:-)
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