Basic HTML version of Foils prepared February 13 00

Foil 19 Example of Communication Overhead

From Master Set for Parallel Programming for Laplace's Equation CPS615 Spring Semester 00 -- February 00. by Geoffrey C. Fox
Largest communication load is communicating 16 words to be compared to calculating 16 updates -- each taking time tcalc
Each communication is one value of ? probably stored in a 4 byte word and takes time tcomm
Then on 16 processors, T16 = 16tcalc + 16tcomm
Speedup S = T1/T16 = 12.25 / (1 + tcomm/tcalc)
or S = 12.25 / (1 + 0.25 tcomm/tfloat)
or S ? 12.25 * (1 - 0.25 tcomm/tfloat)

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