Author: Robert Hyatt
Date: 03:19:47 07/29/98
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On July 29, 1998 at 02:29:38, Amir Ban wrote: >On July 28, 1998 at 18:07:34, Howard Exner wrote: > >>What is the speed difference between the hardware? I'm clueless on >>how fast the 4 200's are in parallel? 2 times, 3 times? > >Having played recently with Crafty (4 x P6/200) and Thoth (supposedly 1 x >P2/400) on ICC, I got the strong impression that Thoth is faster. > >Amir It depends on how/when you play it. IE I have a PII/400 here at the office that I fiddle with from time to time... and it is something like 1.81 times faster than a single pentium-pro. While my 4XP6/200 machine is averaging somewhere in the 3X a single CPU, at strange cases it is no faster, at other equally strange cases it is 4X faster or even faster than that in really bizarre cases. But when you are playing, it depends on *when*. Generally, late at night, you will be playing the full machine. Between 7am and (say) midnight you could be playing either a reduced number of processors (1,2 or 3) or you could be playing the 4-processor code on a machine that isn't getting 4 processors (this is bad and I try to avoid letting it happen, but am not always successful.) I can give you some benchmark resuls if you'd like to see them, but in general, it is hard to guarantee what you are playing against since I use the machine for other things besides chess during the day, and occasionally have students doing things as well (in a parallel processing course.) I did run the kopec suite and post the results a couple of months ago, and produced results about 3x the single-processor version. Also note that in general, SMP works better at deeper searches. It is way more efficient to do 12 ply searches than it is to do 6 ply searches, because it heavily relies on good move ordering to avoid search overhead, and deeper searches make the moves near the root more reliable... As far as Thoth goes, it is very fast. I think I have seen it hit 175K nodes per second. Crafty averages 300K on the full machine, but roughly 1/3 of that is thrown out (not always that much, but its a good pessimistic estimate) leaving 200K effectively. One real killer that happens from time to time is running it in 4X mode, but letting something else run at the same time. Spinlocks make this dangerous and can absolutely crush performance, even when it says "cpu utilization 390%" because a key process could be pre-empted, letting others spin like mad doing nothing at all. Used to kill Cray Blitz if someone sneaked into the machine while we were playing a real game...
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