Messages in this thread | | | From | "Peter T. Breuer" <> | Subject | Re: Interesting scheduling times - NOT | Date | Tue, 22 Sep 1998 11:18:53 +0200 (MET DST) |
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"A month of sundays ago Richard Gooch wrote:" > > > median. Even when I add about 1K interrupts/second, it still varies > > less than 10%. Why does your benchmark vary so much by comparison? > > Why doesn't lmbench vary the same amount? > > See above. The minimum time has a better chance of avoiding cache > pollution/aliasing effects. > > Note: in my tests, I see substantial variance mainly with the process > switching test, not the thread switching test. This is particularly > the case now that Linus posted the FPU saving fix. > On a PPro 180 I'm seeing minimum process switch times of 4.8 us to > 8.5 us. That's a 77% increase. I think that variance is real, and not > an artefact of my test code.
Eh? does anyone know the statistics of the MINIMUM result from N normally distributed tests?
I don't, but since the minimum comes from the tail, it is a rare event and hence its variance must be large.
Your result is what I would naively expect from a normal curve, but I don't believe you have a normal curve. Negative times are impossible :-). You must have a quantized distribution (nano seconds?) with a tail at 0 and +oo. I suppose it's m*exp(-x/m) or something. Can you run some monte carlo simulations with that to get an idea of the distribution of the _minimum_?
Peter
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