Evaluating Coarray Fortran with the CGPOP Miniapp

The Parallel Ocean Program (POP) is a 71,000 line-of-code program written in Fortran and MPI. POP is a component of the Community Earth System Model (CESM), which is a heavily used global climate model. Now that Coarrays are part of the Fortran standard one question raised by POP’s developers is whether Coarrays could be used to improve POP’s performance or reduce its code volume. Although Coarray Fortran (CAF) has been evaluated with smaller benchmarks and with an older version of POP, it has not been evaluated with newer versions of POP or on modern platforms. In this paper, we examine what impacts using CAF has on a large climate simulation application by comparing and evaluating variants of the CGPOP miniapp, which serves as a performance proxy of POP.