Basic HTML version of Foils prepared 14 October 1997

Foil 64 Features of Very Bad Naive Message Parallel Algorithm

From Fox Presentation Fall 1995 CPS615 Basic Simulation Track for Computational Science -- Fall Semester 95/96/97. by Nancy McCracken and Geoffrey C. Fox


1 The parallelism is perfect and both communication and computation are load balanced
2 However messages are small (as described 4 words - a 3 vector Xuse and mass M) and
3 communication » 4 tcomm(for small messages)
4 where estimate ~15 tfloat could be higher depending on how 1/ri,j3 calculated. As involves division and square root, it is expensive if done directly. Sometimes better to calculate by table lookup but this involves slow memory access
5 As typically tcomm/tfloat » 10 even for quite large messages (and worse for small ones), the above estimate suggests that communication dominates ...

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