Improving ocean modeling software NEMO 4.0 benchmarking and communication efficiency

Abstract. Communications in distributed memory supercomputers are still limiting scalability of geophysical models. Considering the recent trends semiconductor industry, we think this problem is here to stay. We present optimizations that have been implemented 4.0 version ocean model NEMO improve its scalability. Thanks collaboration oceanographers and HPC experts, identified removed unnecessary communications two bottleneck routines, computation free surface pressure gradient, forcing straight or unstructured open boundaries. Since a wrong parallel decomposition choice could undermine computing performance, impose automatic definition all cases, including when subdomains containing land points only excluded from decomposition. For smaller audience developers vendors, propose new benchmark configuration, which easy use while offering full complexity operational versions.