High-Productivity Framework on GPU-Rich Supercomputers for Operational Weather Prediction Code ASUCA

The weather prediction code demands large computational performance to achieve fast and high-resolution simulations. Skillful programming techniques are required for obtaining good parallel efficiency on GPU supercomputers. Our framework-based weather prediction code ASUCA has achieved good scalability with hiding complicated implementation and optimizations required for distributed GPUs, contributing to increasing the maintainability, ASUCA is a next-generation high resolution meso-scale atmospheric model being developed by the Japan Meteorological Agency. Our framework automatically translates user-written stencil functions that update grid points and generates both GPU and CPU codes. User-written codes are parallelized by MPI with intra-node GPU peer-to-peer direct access. These codes can easily utilize optimizations such as overlapping technique to hide communication overhead by computation. Our simulations on the GPU-rich supercomputer TSUBAME 2.5 at the Tokyo Institute of Technology have demonstrated good strong and weak scalability achieving 209.6 TFlops in single precision for our largest model using 4,108 NVIDIA K20X GPUs.