Directive-Based Parallelization of the NIM Weather Model for GPUs

Abstract

The NIM is a performance-portable model that runs on CPU, GPU and MIC architectures with a single source code. The single source plus efficient code design allows application scientists to maintain the Fortran code, while computer scientists optimize performance and portability using OpenMP, OpenACC, and F2C-ACC directives. The F2C-ACC compiler was developed in 2008 at NOAA's Earth System Research Laboratory (ESRL) to support GPU parallelization before commercial Fortran GPU compilers were available. Since then, a number of vendors have built GPU compilers that are compliant to the emerging OpenACC standard. The paper will compare parallelization and performance of NIM using the F2C-ACC, Cray and PGI Fortran GPU compilers.