Author: Tord Romstad
Date: 07:15:44 09/26/03
Go up one level in this thread
On September 26, 2003 at 07:01:49, Ricardo Gibert wrote: >On September 25, 2003 at 13:02:22, Tord Romstad wrote: > >>On September 25, 2003 at 11:28:55, Robert Hyatt wrote: >> >>>On September 25, 2003 at 09:48:33, Tord Romstad wrote: >>> >>>>On September 24, 2003 at 16:28:57, Robert Hyatt wrote: >>>> >>>>>I try to use _most_ of main memory for serious games, and if you have a >>>>>1 gig machine, I generally use something like hash=784M, hashp=40M, >>>>>cache=128M, and go from there... >>>> >>>>Interesting. Is a 40M pawn hash table really useful for Crafty? How big >>>>are your pawn hash entries? My pawn hash table contains just 256 entries, >>>>where each entry is 128 bytes. The last time I tried, increasing the size >>>>of the table gave just a very small speedup (less than 2%, if I recall >>>>correctly). >>>> >>>>Tord >>> >>> >>>I've never carefully tested this, but 256 entries seems _way_ small. Just >>>look at how many different possible pawn positions there are. >> >>I decided to experiment with this again. I let my engine analyze the >>position after 1. d4 d5 2.c4 e6 3. Nc3 Nf6 4. Bg5 Be7 to a depth of >>10 plies with different pawn hash table sizes. Here are the results >>(the first column is the number of entries, the second column is the >>number of seconds needed to complete 10 plies): >> >> 1 70.59s >> 2 60.08s >> 4 58.28s >> 8 57.25s >> 16 55.74s >> 32 55.24s >> 64 54.38s >> 128 54.18s >> 256 53.76s >> 512 53.53s >> 1024 53.32s >> 2048 53.05s >> 8192 52.68s >> 16384 52.25s >> 32768 52.09s >> 65536 51.87s >>131072 51.82s >>262144 51.85s >>524288 51.88s >> >>As you can see, the speed gain by increasing the number of entries from >>256 is not very big, and increasing the size beyond 65536 entries seems >>completely useless. >> >>Of course, it is possible that a different position would have given >>different results. >> >>Tord > >This is a surprise! If your results are replicated by other programs, it would >be *very* interesting. Yes, I would also be interested in seeing results from other programs. >Have you any insights on why a bigger phash is not really >useful? My pawn hash table is an always-replace table (I assume everybody does this). This means that it always contains the last 256 pawn structures seen in the search tree. It seems reasonable to me that the probability that the current pawn structure has occured also in some recently visited node is very high, because nodes which are close to each other in the tree tend to have similar pawn structures. Tord
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