Messages in this thread | | | Date | Mon, 30 Aug 2010 14:21:38 +0100 | From | Matt Fleming <> | Subject | Re: [RFC][PATCH 2/5] perf: Turn the group counter values into delta values |
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On Mon, Aug 30, 2010 at 02:54:01PM +0200, Peter Zijlstra wrote: > On Mon, 2010-08-30 at 13:13 +0100, Matt Fleming wrote: > > Change the semantics of the PERF_FORMAT_GROUP records and make them > > delta values, i.e. the difference in value between consecutive reads of > > the hardware counters. These delta values will be used in a subsequent > > patch to calculate weighted values (by multiplying the deltas with the > > time difference between reads of the counters). Calculating these deltas > > is easiest to do in the kernel (as opposed to the userland tools) > > because we can reset the counter whenever we read from it. > > > > Note that even though this patch changes the semantics of > > PERF_FORMAT_GROUP records there were no users of them anyway (the tools > > didn't even understand them). > > libpfmon might be using it,.. I know some people occasionally reported > bugs for this so there are users. > > Also, there's no real synchonization between read,read and read,sample > so its racy to do this, simply generate deltas in post-processing.
Ah, fair enough. Thanks, I'll do this with post-processing.
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