Performance portability of an intermediate-complexity atmospheric research model in coarray Fortran

We examine the scalability and performance of an open-source, coarray Fortran (CAF) mini-application (mini-app) that implements the parallel, numerical algorithms that dominate the execution of The Intermediate Complexity Atmospheric Research (ICAR) [4] model developed at the the National Center for Atmospheric Research (NCAR). The Fortran 2008 mini-app includes one Fortran 2008 implementation of a collective subroutine defined in the Committee Draft of the upcoming Fortran 2018 standard. The ability of CAF to run atop various communication layers and the increasing CAF compiler availability facilitated evaluating several compilers, runtime libraries and hardware platforms. Results are presented for the GNU and Cray compilers, each of which offers different parallel runtime libraries employing one or more communication layers, including MPI, OpenSHMEM, and proprietary alternatives. We study performance on multi- and many-core processors in distributed memory. The results show promising scaling across a range of hardware, compiler, and runtime choices on up to ~100,000 cores.