Evaluating the Performance of Software Distributed Shared Memory as a Target for Parallelizing Compilers

In this paper, we evaluate the use of software distributed shared memory (DSM) on a message passing machine as the target for a parallelizing compiler. We compare this approach to compiler-generated message passing, hand-coded software DSM, and hand-coded message passing. For this comparison, we use six applications: four that are regular and two that are irregular. Our results are gathered on an 8-node IBM SP/2 using the TreadMarks software DSM system. We use the APR shared-memory (SPF) compiler to generate the shared memory programs, and the APR XHPF compiler to generate message passing programs. The hand-coded message passing programs run with the IBM PVMe optimized message passing library. On the regular programs, both the compilergenerated and the hand-coded message passing outperform the SPF/TreadMarks combination: the compiler-generated message passing by 5.5% to 40%, and the hand-coded message passing by 7.5% to 49%. On the irregular programs, the SPF/TreadMarks combination outperforms the compiler-generated message passing by 38% and 89%, and only slightly underperforms the hand-coded message passing, differing by 4.4% and 16%. We also identify the factors that account for the performance differences, estimate their relative importance, and describe methods to improve the