High-Performance Coarray Fortran Support with MVAPICH2-X: Initial Experience and Evaluation

Coarray Fortran (CAF) is a parallel programming paradigm that extends Fortran for the partitioned global address space (PGAS) programming model at the language level. The current runtime implementations of CAF are mainly using MPI or GASNet as underlying communication components. MVAPICH2-X is a hybrid MPI+PGAS programming library with a Unified Communication Runtime (UCR) design. In this paper, the classic implementation of CAF runtime in Open UH is redesigned and rebuilt on top of MVAPICH2-X. The proposed design does not only enable the support of MPI+CAF hybrid programming model, but also provides superior performance on most of the CAF one-sided operations and the newly proposed collective operations in Fortran 2015 specification. A comprehensive evaluation with different benchmarks and applications has been performed. Comparing with current GASNet-based solutions, the CAF runtime with MVAPICH2-X can improve the bandwidths of put and bidirectional operations up to 3.5X for inter-node communication, and improve the bandwidths of collective communication operations represented by broadcast up to 3.0X on 64 processes. It also reduces the execution time of NPB CAF benchmarks by up to 18% on 256 processes.