Author: Uri Blass
Date: 11:23:51 09/01/03
Go up one level in this thread
On September 01, 2003 at 13:20:48, Michael P. Nance Sr. wrote: >On August 31, 2003 at 21:18:58, Ross Boyd wrote: > >>On August 31, 2003 at 19:44:28, William Penn wrote: >> >>>The more hash I allocate, the slower the kN/s speed. Thus 4MB (the minimum) is >>>the fastest in my tests, typically about 450kN/s. If I increase that to say >>>256MB hash, the speed slows down to about 400kN/s. The more I increase hash, the >>>slower the kN/s speed. >>> >>>The kN/s speed peaks, then eventually starts to decrease. How long this takes >>>depends on the amount of hash. However in my tests, the long term speed >>>advantage of bigger hash never catches up with the long term speed obtained with >>>smaller hash. Thus I don't see any advantage whatsoever to using a hash table! >>>The opposite seems to be true!? >>> >>>I'm using the Shredder7 GUI, Shredder 7.04 UCI engine, AMD XP Athlon 2400+/640MB >>>RAM (608MB available). The GUI says the maximum I can allocate to hash is about >>>455MB, so I'm not near the limit. Of course I'm using fairly common practical >>>positions for these tests in Infinite Analysis mode, and the above indicated >>>results are typical. >>> >>>I get very similar results running Shreddermarks with different size hash. The >>>more hash, the lower the Shreddermark and corresponding kN/s. >>> >>>Now, will someone please refute this, or explain what I'm missing or >>>overlooking? Thanks! >>>WP >> >>Increasing the hash size will tend to lower the NPS in most engines. >> >>Its kind of hard to explain why this is so... but I'll try. When an engine gets >>a hit in the hashtable it often cuts short the amount of exhaustive quiescence >>searching where NPS tends to go high. Nearer the root there is generally more >>overhead involved, with for example, more sophisticated move ordering etc... >>whereas the move ordering at the QS tends to be cruder and hence faster. >> >>Anyway, its not a bad thing.... >> >>What is more important is the total number of nodes visited to get to a certain >>depth. You will see that increasing hash size will tend to reduce the tree... >>and therefore (even though NPS drops slightly) the actual time taken to get to a >>given depth is reduced (usually). >> >>Time how long Shredder takes to get to a given depth, and also the total nodes >>visited, with various positions for two hash sizes. You'll see the true benefit >>of increasing the hash size. >> >>If you turn off the hash altogether you'll see the NPS increase a lot... but its >>not going to play stronger that's for sure... >> >>So, NPS is not a measure of strength. Really, its only useful for comparison >>purposes of the same engine with the same hash size on 2 different PCs. >> >>Hope this makes sense... >> >>Ross > >I will tell You this,when I demisish the Hash,(32,64,128,ect),I get beat. When I >go "FULL THROTTLE",or optimise the Hash,(819), I usually beat the same Box and >Program that I couldn't beat with a lower Hash setting.>>>>Mike I am not surprised. If you give your program a big hash table and another application is running the big hash tables is too much and it needs to read from the hard disk so it may become very slow. I suggest not to give your program more than 1/2 of the RAM of your machine. The possible advantage of few elo points is not enough to complensate for the risk. You may even decide not to give more than 1/4 of the RAM of your machine and still the program play at almost optimal strength. Uri
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