Author: Anthony Cozzie
Date: 07:52:57 12/19/03
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On December 19, 2003 at 10:41:27, Robert Hyatt wrote: >On December 19, 2003 at 01:21:45, Jouni Uski wrote: > >>After installing more RAM to my Pentium 2,4 GHz I tested Fritz8 in some test >>suites with 128MB and 384MB hash (time limit was 10 minutes and positions quite >>hard = average solution times around 3-5 minutes): to my surprise >>average solution time was shorter with 128MB! Why? Absolutely no hard disk >>swapping with 512MB total RAM! >> >>Jouni > > >Hashing is based on random numbers. Which means the result of using them >is going to have a bit of randomness as well. Sometimes bigger hash slows >a program down, because it makes the search more accurate, which might make >it a bit slower. But accuracy and speed don't necessarily match up so it is >not easy to say "this is slower, so it is worse." > >Also, there are hardware considerations. The size of the TLB for example. >If you blow that out, you make your memory access time go from maybe 150ns >to 3X that. Since hash tables are addressed randomly, this is a real >possibility. IE the opteron I was using earlier this week has just over >1000 TLB entries. That lets me address 1000 * 4K very quickly. Anything >beyond that sees slower memory access times. there is a patch for 2.6 that will automatically use the large pages. that plus prefetching should give quite a speedup to crafty . . . anthony
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