Performance Comparison of Three Parallel Implementations of a SchwarzSplitting Algorithm

We describe three implementations of a Schwarz splitting algorithm for the numerical solution of two dimensional, second-order, linear elliptical partial differential equations. One implementation makes use of the SCHEDULE package. A second uses the language extensions available in SEQUENT Fortran for creating and controlling parallel processes. The third implementation is a hybrid of the first two -- using explicit (non-portable) calls to create a control parallel processes, but using data structures and overhead similar to the implementation that uses SCHEDULE. We report from several experiments with typical test problems on a Sequent Symmetry S81 shared-memory multiprocessor. We measure the overhead involved in using SCHEDULE, and discuss advantages and disadvantages of this approach.