Author: Matthew Hull
Date: 06:02:28 09/03/03
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On September 03, 2003 at 00:07:37, Jeremiah Penery wrote: >On September 02, 2003 at 22:54:49, Robert Hyatt wrote: > >>Maybe. But I use threads. And on NUMA threads are _bad_. One example, >>do you _really_ want to _share_ all the attack bitmap stuff? That means it >>is in one processor's local memory, but will be slow for all others. What >>about the instructions? Same thing. > >After some thinking, it seems to me that the *average* memory access speed will >be the same no matter where the data is placed, for anything intended to be >shared between all processors (in a small NUMA configuration). The reason for >this is because what is local to one processor will be non-local to all others. >It doesn't matter if everything is local to the same processor or spread around, >because the same percentage of total accesses will be non-local in any case >(unless there is a disparity between the number of accesses each CPU is trying >to accomplish). > >The only problem is that one processor's memory banks might get hammered, but >that _is_ the same with an (similarly small) SMP configuration - all accesses go >serially through one memory controller. > >As machine size increases, of course, NUMA can run into more problems. But then >SMP has its own problems as well (cost and complexity of memory sub-system, >mostly). But for chess, each piece of the search process will be on it's own processor and all the data it needs to do the search will be copied once at the start of it's "assignment", then it's off to the races. The only time he needs to use non-local memory is at the start (copy) and the end (report results). Yes? MH
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