Dolphin Wulfkit
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Greg Lindahl lindahl at keyresearch.comFri May 3 13:58:28 PDT 2002
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On Fri, May 03, 2002 at 09:54:30AM +0200, Joachim Worringen wrote: > Regarding the placement of the process (or: assignment of ranks) on > SMP-nodes is part of the peformance strategiy that an MPI library is > free to follow. It seems that ScaMPI does a straight round-robin mapping > of the process-to-node-ranks, while MPICH-GM "groups" processes on the > same node. Both approaches are, of course, valid. If a benchmark measures process-to-process bandwidth and latency between only 2 processes, it matters whether or not they are on the same node (shmem) or not. It's not a matter of round robin vs. groups. BTW, groups _are_ strongly preferred, but that's not the issue. Why? If you have a program that does nearest neighbor communication, where are your neighbors? With round robin you are accessing your array in the wrong order. greg
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