Author: Sune Fischer
Date: 10:03:16 05/03/04
Go up one level in this thread
On May 03, 2004 at 11:13:11, Vincent Diepeveen wrote: >On May 03, 2004 at 10:53:19, Robert Hyatt wrote: > >>On May 03, 2004 at 10:19:46, Sune Fischer wrote: >> >>> >>>>I don't see any at 8. I don't personally have access to a 16-way box yet so I >>>>can't say anything there. But there is nothing that really makes null-move hurt >>>>parallel search... >>> >>>Couldn't it be, that nullmove hurts scalability in much the same way alpha-beta >>>"hurts" parallel search compared to minimax? >> >>I don't see how. It might make _some_ positions more unstable, and unstable >>positions hurt parallel search. But it also makes other positions more stable. > >What a nonsense. "i don't see how." > >it is very clearly proven. For everyone doing parallel research it is *trivial* >that more unstable trees are harder to split. Yes I think that is trivial too, but what is not so trivial is if nullmove causes these unstable search trees. >Further you must wait *longer* now to split because you first nullmove and must >search another move before splitting. Yes, but wouldn't this result in some processors running idle? >>I don't see why, unless you form the hypothesis of "forward pruning makes move >>ordering _worse_." That's the only wat this could happen... >> >>There are obviously "issues". Forward pruning tosses moves out. So at any node >>you will have fewer branches to search than in a normal (non-pruning) program. >>But if you don't require that all processors always work at the same node, this >>should not be a problem. IE Crafty searches endgames just as efficiently as it >>searches complex middlegames, from an SMP perspective... > >In endgames you search in general bigger depths. So on average the trees that >are there after you split are bigger. Bigger depthleft means less overhead and >more efficient parallel search. That sounds logical, but I think splitting overhead << parallel search overhead, so there must be another explanation too. I seem to recall some numbers from Crafty, that a split is basicly a copy of a few kilobytes and a split happens a few thousand times a minute. This would accumulate to 1 second CPU time? -S.
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