Author: Vincent Diepeveen
Date: 06:03:21 04/15/03
Go up one level in this thread
On April 15, 2003 at 04:54:11, Tony Werten wrote: >On April 14, 2003 at 17:43:12, Robert Hyatt wrote: > >>On April 14, 2003 at 17:15:41, Vincent Diepeveen wrote: >> >>>On April 13, 2003 at 22:39:39, Robert Hyatt wrote: >>> >>>>On April 13, 2003 at 11:49:28, Vincent Diepeveen wrote: >>>> >>>>>On April 13, 2003 at 11:27:53, Robert Hyatt wrote: >>>>> >>>>>I said initially. It drops back to 10 splits a second in DIEP after a while. >>>>>Search depth matters. >>>>> >>>>>Let's compare 2 things. >>>>> >>>>> time=45.98 cpu=464% mat=0 n=37870294 fh=88% nps=823k >>>>> ext-> chk=638414 cap=249442 pp=9588 1rep=32966 mate=223 >>>>> predicted=0 nodes=37870294 evals=14565859 >>>>> endgame tablebase-> probes done=0 successful=0 >>>>> hashing-> trans/ref=28% pawn=93% used=28% >>>>> SMP-> split=431 stop=57 data=6/64 cpu=3:33 elap=45.98 >>>>> >>>>>MT 2 crafty 18.10 which i have here. 431 splits at 45 seconds. I guess you must >>>>>limit in crafty the number of splits a lot as splitting is expensive in crafty >>>>>when compared to the costs of a single node. >>>> >>>>I'm not sure how expensive it is compared to a node. I'll run a test where >>>>I do the split overhead at every node to compare, however... >>>> >>>> >>>> >>>>I don't limit them at all. The only limit is the YBW algorithm. But I split >>>>at the root also, which reduces them signficantly... >>> >>>I can split at the root nowadays, but i have turned it off for diep. it gives >>>too poor speedup for me. The interesting thing which searching SMP can give is >>>transpositions at a big depth which possibly are overwritten by a sequential >>>search. i don't want to miss them. >> >>Maybe you don't split at the root correctly. I limit this with some intelligent >>guesswork, so that if it appears that I might change my mind this iteration, >>then >>I don't split at the root until I have searched all moves that I think might >>replace >>the best move... > >Just trying to understand. Are you talking about the case where the best move in >the root got a fail low ? this has not so much to do with alfabeta but with how you parallel split. After the best move has been searched (YBW property) so after you have a mainline, then the rest of the moves can be searched in parallel according to YBW algorithm. Bob is doing that in crafty (with usually 3 moves for the YBW property and not 1, as nullmove counts too as a move. I'm using 2, that includes nullmove). I'm not doing that in Diep as it gives me a bad parallel performance. For fritz&co it didn't give a good speedup either. Of course i did mainly dual cpu tests here. not many 16 processor tests. I can get a 16 processor NUMA machine for > 90% busy effectively even with 2 cpu's at 1 position, so no need at all to split at root at all. So no need to try if it already gives a poor speedup at 2 processors. However with 128 processors or so it might be a good idea to re-experiment with this as it is hard to get cpu's busy. Crafty on other hand doesn't have a very good speedup at 2 processors and the price of a split is expensive, so probably Bob concluded something else than i did. > >When that happens, your testresults indicate that's it's better to split lower >than to search 2 rootmoves parallel in order to get an established score asap ? >( So not breaking off seacrh when 1 gets a first failhigh, but only when the >score is resolved ) >Tony > >> >> >>>
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