Performance of Fortran Coarrays on the Cray XE6

Coarrays are a feature of the Fortran 2008 standard that enable parallelism using a small number of additional language elements. The execution model is that of a Partitioned Global Address Space (PGAS) language. The Cray XE architecture is particularly interesting for studying PGAS languages: it scales to very large numbers of processors; the underlying GEMINI interconnect is ideally suited to the PGAS model of direct remote memory access; the Cray compilers support PGAS natively. In this paper we present a detailed analysis of the performance of key coarray operations on XE systems including the UK national supercomputer HECToR, a 90,000-core Cray XE6 operated by EPCC at the University of Edinburgh. The results include a wide range of communications patterns and synchronisation methods relevant to real applications. Where appropriate, these are compared to the equivalent operation implemented using MPI. Keywords-Fortran; parallel programming; benchmark.