Author: Robert Hyatt
Date: 09:15:37 12/19/03
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On December 19, 2003 at 10:52:57, Anthony Cozzie wrote: >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 I know. I have mentioned that in the past already. However, on my xeon, the usual memory benchmark program only reports something like 60 TLB entries, which seems low (lmbench). I have not tried 2.6 on my machine, as it isn't just a matter of grabbing and building the kernel, there are a bunch of other things including binutils, and the like, that also have to be upgraded. I hope someone will do a 2.6 distribution before long and I'll dive in. the 4M page size sounds pretty good, from a memory access point of view (not thrashing the TLB so badly).
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