> : I only mentioned that because Larry mentioned normal distributions of
> : results in a previous message and it struck me as strange to expect a
> : normal distribution of scheduler latencies. He was arguing against using
> : the minimum time from a benchmark, as I recall. There are a number of
> : places this is useful number, for instance, the round trip times from
> : ping. The minimum rtt is a rather hard limit and tells you what the best
> : latency you can expect is.
>
> Well, this is a fine theory - and it was what I thought when I started
> measuring things - but it's wrong in practice. If you take a suite of
> tests, lmbench for example, and do a bunch of runs and scatter plot them
> and stare at them you'll see patterns emerging. Now if the pattern was
> that most run times clustered around the min, then my feeling is that
> the min is the right number. Wherever they cluster up is the number I
> wanted because that was the number mostly likely to be seen.
Again, I agree that generally the average is the number that's
interesting. But earlier you seemed to imply that the minimum is not
generally a meaningful number, because they were way out on the tails of
normal distributions. Even if that is true (and many distributions that
are the combination of many events will take a bell shaped curve because
of the binomial theorem, but at the same time many aren't), that doesn't
mean that the minimum is meaningless. It may generally be a poor number to
use for benchmarks, but it may be able to tell you about room for
improvement, underlying physical constraints, etc. See the ping example.
-- "Love the dolphins," she advised him. "Write by W.A.S.T.E.."
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