Author: Robert Hyatt
Date: 16:57:23 09/03/03
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On September 03, 2003 at 18:57:06, Jeremiah Penery wrote: >On September 03, 2003 at 13:06:34, Robert Hyatt wrote: > >>The point for the "Crafty algorithm" is that I rarely share things among >>_all_ processors, except for the transposition/refutation table and pawn >>hash table. >> >>Split blocks are shared, but explaining the idea is not so easy. But to >>try: >> >>When a single processor is searching, and notices that there are idle >>processors, it takes its own split block, and copies the data to N new >>split blocks, one per processor. For all normal searching, each processor >>uses only its own split block, except at the position where the split >>occurred. There the parent split block is accessed by all threads to get >>the next move to search. That is not a very frequent access. And there, >>there will be penalties that are acceptable. But for the _rest_ of the >>work each processor does, I used a local split block for each so that they >>ran at max speed. That was the main change... >> >>Without that "fix" it ran very poorly. There was so much non-local memory >>traffic that performance was simply bad. With the fix, things worked much >>better. > >That's how I assumed it always worked anyway, with each processor using only its >own split block, so that there wouldn't be very many non-local accesses. From >that perspective, there are very few non-local accesses (as you say), and NUMA >doesn't cause much problems. It _could_ work that way. IE right now I have split blocks that are in a big array. They don't have to be. They could allocated locally on each processor, so that the first N are local to processor 0, the next N are local to processor 1, etc. Then the problem goes away. Unfortunately I didn't design it like that, but the change is not very difficult to do... But there is no real benefit until I get my hands on a real NUMA box (again) to play with... > >I guess my assumption was wrong about that, and I've been arguing from that >position. Thanks for the explanation.
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