Author: Vincent Diepeveen
Date: 18:46:52 09/28/02
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On September 27, 2002 at 23:29:58, Anthony Cozzie wrote: >Recently, I profiled my chess engine, and one function in particular stood out. >The transposition probe function takes about 7% of the CPU time, or about 350 >cycles/call. All it does is access the transposition table, but the random >nature of the accesses means that it usually misses in the cache AND the TLB, >thus requiring 2 memory accesses at 100+ cycles each. 300+ clocks for a single random cache line is exactly what sounds typical for a lookup from a fast 1.xx Ghz K7 processor to RAM. I'm amazed it isn't 400+ clocks actually. probably because you have fast RAM? i use registered ddr ram for a dual k7. is 1 clock slower in latency if i remember well. >In my engine, the search function generates the next move, makes the next move, >checks if it is legal, checks if the opponent is in check, and recurses, so >there are two calls to is_check() between when the transposition key is >available and when the key is used. I tried inserting a prefetch instruction [I >run an Athlon] with absolutely no effect. I even tried following the prefetch >with a long loop to make SURE it would have enough time to access the memory, >with no results. Lastly I tried a MOV instruction, also with no result. Am I >just doing something wrong here? > >Has anyone else tried to something similar with better results?
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