Porting the Meso-NH atmospheric model on different GPU architectures for the next generation of supercomputers (version MESONH-v55-OpenACC)

Abstract. The advent of heterogeneous supercomputers with multi-core central processing units (CPUs) and graphics processing units (GPUs) requires geoscientific codes to be adapted to these new architectures. Here we describe the porting of the Meso-NH version 5.5 community weather research code to GPUs named MESONH-v55-OpenACC, with guaranteed bit reproducibility thanks to its own MPPDB_CHECK library. This porting includes the use of OpenACC directives, specific memory management, communications optimization, development of a geometric multigrid solver and creation of an in-house preprocessor. Performance on AMD MI250X GPU Adastra platform shows up to 6.0× speedup (4.6x on NVIDIA A100 Leonardo platform), and achieves a gain of a factor 2.3 in energy efficiency compared to AMD Genoa CPU Adastra platform, using the same configuration with 64 nodes. The code is even 17.8 faster by halving the precision and quadrupling the nodes with a gain in energy efficiency of a factor 1.3. First scientific simulations of three representative storms using 128 GPUs nodes of Adastra show successful cascade of scales for horizontal grid spacing down to 100 m and grid size up to 2.1 billion points. For one of these storms, Meso-NH is also successfully coupled to the WAVEWATCH III wave model via the OASIS3-MCT coupler without any extra computational cost. This GPU porting paves the way for Meso-NH to be used on future European exascale machines.