Experiences with Co-array Fortran on Hardware Shared Memory Platforms

When performing source-to-source compilation of Co-array Fortran (CAF) programs into SPMD Fortran 90 codes for shared-memory multiprocessors, there are several ways of representing and manipulating data at the Fortran 90 language level. We describe a set of implementation alternatives and evaluate their performance implications for CAF variants of the STREAM, Random Access, Spark98 and NAS MG & SP benchmarks. We compare the performance of library-based implementations of one-sided communication with finegrain communication that accesses remote data using load and store operations. Our experiments show that using application-level loads and stores for fine-grain communication can improve performance by as much as a factor of 24; however, codes requiring only coarse-grain communication can achieve better performance by using an architecture’s tuned memcpy for bulk data movement.