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Subject: Re: Crap statement refuted about parallel speedup

Author: Dave Gomboc

Date: 20:30:51 09/18/01

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On September 18, 2001 at 18:27:01, Robert Hyatt wrote:

>Before you label a statement as ridiculous, find me _one_ person that will
>side with you and say that "yes, it is possible to get a > 2 speedup using
>only two cpus on anything but anomaly positions.  Find _one_ person that will
>agree...

This is (okay, not very!) amusing... the statement is the exact opposite of
reality, which (as Bob already knows) is that "it is only possible to get a < 2
speedup using only two cpus on anything but anomaly positions".

If a parallel algorithm consistently outperformed a sequential algorithm, then
you've just discovered a better sequential algorithm as well (use time-slicing).
 If you then don't use this better sequential algorithm to compare your parallel
algorithm against, you'd be comparing a good parallel algorithm against a shitty
sequential algorithm, which would make the speedup result worthless.

It is absolutely key that when people compare their parallel algorithm to their
sequential algorithm that they compare the best possible sequential algorithm.
There are more than a few papers that don't do this... thankfully, at least some
of them have been rejected.

Dave



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