Author: Tony Werten
Date: 04:18:28 09/19/01
Go up one level in this thread
On September 18, 2001 at 18:27:01, Robert Hyatt wrote: >On September 18, 2001 at 17:19:54, Vincent Diepeveen wrote: > >>On September 18, 2001 at 16:53:30, Robert Hyatt wrote: >> >>>On September 18, 2001 at 14:45:45, Vincent Diepeveen wrote: >> >>[snip] >> > >That is correct. If you can produce a speedup of > 2x, using 2 cpus, you >have a bug, or an anomaly position. It is simply not possible. If you >are _really_ doing that, you should modify your single-cpu version as >follows: > >search normally until you would choose to use a second process if you had one. >From this point forward, time-slice between two search threads. Search one >node on one, one on the other. That should run twice as fast, since it is >_exactly_ how the program really does on the SMP platform. > >And that will _not_ work unless you have either the world's worse sequential >search algorithm, or the world's buggiest parallel search algorithm. > >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... > Just for fun, I'll give it a try. I'm probably wrong but maybe you can point out where I go wrong. To make it more obvious I'll make the numbers a bit more extreme. Vincent says that in 85% of the cases the first move is the cutoff move, that means in 15% it's not. Now suppose the cutoff move is always the second move and that it's an easy cutoff. Normally you would search the first move (say 15 seconds) then the second (say 5 sec) total is 20. Now 1st and second are searched parallel, second causes cutoff after 5 secs, first get's stopped. Total time 5 secs. 4 times faster. Funny thing: The worse your first cutoff rate is, the bigger the speedup. cheers, Tony
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