On Thu, 2012-09-06 at 14:25 -0700, Paul E. McKenney wrote: > On Thu, Sep 06, 2012 at 08:41:09PM +0200, Peter Zijlstra wrote: > > On Thu, 2012-09-06 at 17:46 +0200, Jiri Olsa wrote: > > > The 'perf diff' and 'std/hist' code is now changed to allow computations > > > mentioned in the paper. Two of them are implemented within this patchset: > > > 1) ratio differential profiling > > > 2) weighted differential profiling > > > > Seems like a useful thing indeed, the explanation of the weighted diff > > method doesn't seem to contain a why. I know I could go read the paper > > but... :-) > > Or you could ask the author. ;-) > > Ratio can be fooled by statistical variations on profiling buckets with > few counts. So if you are looking for a 10% difference in execution > overhead somewhere in a large program, ratio will unhelpfully sort a > bunch of statistical 2x or 3x noise to the top of the list. > > So you could use the difference in buckets instead of the ratio, but this > has problems in the case where the two runs being compared got different > amounts of work done, as is usually the case for timed benchmark runs > or throughput-based benchmark runs. In these cases, you use the work > done (or the measured throughput, as the case may be) as weights. > The weighted difference will then pinpoint the code that suffered the > greatest per-unit-work increase in overhead between the two runs.
Ah, ok, I guess that makes sense. Thanks! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
