Author: Robert Hyatt
Date: 08:09:21 09/02/03
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On September 01, 2003 at 23:58:38, Jeremiah Penery wrote: >On September 01, 2003 at 23:53:20, Robert Hyatt wrote: > >>It is almost guaranteed that _all_ critical search data for _all_ threads will >>be allocated in a single processor's local memory. > >That would be the worst possible usage of memory. Why in the world would a >program perform like that? Do you understand how parallel programming works? Suppose you want to do this: TREE blocks[128]; Where TREE is a big structure. That puts the blocks into consecutive memory addresses. On a NUMA machine that puts the blocks into one processor's local memory, or it might split across two if you are near the end of one's memory. On a true SMP (non-NUMA) box, that works _perfectly_ and it is the way things are done. On a NUMA box, it sucks. As I said, it takes a _redesign_ of how memory is used, to make a NUMA box run efficiently. Assumptions that are fine on any SMP box fail on a NUMA box. IE Crafty runs just fine on a 32 CPU T90 from Cray. But it uses a crossbar memory switch, not NUMA. Ditto for my dual/quad boxes here.
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