Author: Matthew Hull
Date: 20:56:50 09/03/03
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On September 03, 2003 at 19:57:23, Robert Hyatt wrote: >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. Would this also help people with dual Athlon boxes to get better speedup? MH
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