Impact of the Implementation of MPI Point-to-Point . . .

We examine the send and receive mechanisms of MPI and how to implement message passing robustly so that performance is not signicantly aected by changes to the MPI system. We discuss this within the context of two dierent parallel algorithms for sparse Gaussian elimination: a multifrontal solver (MUMPS), and a supernodal one (SuperLU). The performance of our initial strategies based on simple MPI point-to-point communication primitives is very sensitive to the MPI system, particularly the way MPI buers are used. Using more sophisticated nonblocking communication primitives improves the performance robustness and scalability, but at the cost of increased code complexity