Messages in this thread | | | Subject | Re: [PATCH 4/4][RFC] perf_counter: Allow sharing of output channels | From | Peter Zijlstra <> | Date | Thu, 20 Aug 2009 12:24:32 +0200 |
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On Thu, 2009-08-20 at 12:13 +0200, stephane eranian wrote: > On Wed, Aug 19, 2009 at 2:56 PM, Peter Zijlstra<a.p.zijlstra@chello.nl> wrote: > > On Wed, 2009-08-19 at 22:36 +1000, Paul Mackerras wrote: > >> Peter Zijlstra writes: > >> > >> > Provide the ability to configure a counter to send its output to > >> > another (already existing) counter's output stream. > >> > >> What sort of thing might this be useful for? > > > > Some people complained that its tedious to mmap() for every counter and > > would like to share the mmap() output buffer between counters. > > > > > This saves on address space and mlock budget and I guess fd management > > logic. > > > Interesting to see, you seem to have changed your mind on this.
Lets say I haven't quite made up my mind yet, but people seem to want it.
> I recall pointing this out in my early comments.
Yeah :-)
> But anyway, here are some more comments: > > - how does this work with the remapped counts? > Probably only see the count for the target, i.e., output, event
Ah, right you are, we'd have to allow mmap() of the first page but no data section.
> - if samples from multiple events end up in the same buffer, how do > I tell them apart, > i.e., how do I know sample X came from event A, sample X from event B? > This may be useful to detect patterns.
PERF_SAMPLE_ID?
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