Parallel Computer Architecture

7.8 Implications for Parallel Software 537

clearly visible, repeating in a regular pattern with the two smaller sizes more com-

mon than the larger one. Overall, there is substantially more white space than dark,

so the average communication bandwidth is more of an indication of the ratio of com-

munication to computation than it is of the rate of communication during a commu-

nication phase.

If we apply the framework provided by Equation 3.1 to the speedup measure-

ments on the NAS parallel benchmarks, we find that all of the parallelism costs

increase with the number of processors. The extra work increases, the amount of

communication increases ...