Dual-Level Parallel Analysis of Harbor Wave Response Using MPI and OpenMP.

The authors describe their experiences converting an existing serial production code to a parallel code combining both MPI and OpenMP. Such dual-level parallel codes will be able to take full advantage of the emerging class of high performance computer architectures using small clusters of shared-memory processors connected via a message-passing network. While the focus is restricted to a harbor response simulation code, the techniques presented herein are appropriate for a broad class of applications that explore a parameter space. The code modifications reduced the execution time of one test case from 3100 minutes on a single CPU to just over 12 minutes on 256 CPUs. Results demonstrate that dual-level parallelism allows substantial increases in model resolution combined with improvements in simulation turnaround time but, contrary to conventional wisdom, requires very little source code alteration.