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 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 (MG) solver and creation of an in-house preprocessor. Performance on the AMD MI250X GPU Adastra platform shows up to 6.0× speedup (4.6× on the NVIDIA A100 Leonardo platform), and achieves a gain of a factor of 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 of 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.