swLICOM: the multi-core version of an ocean general circulation model on the new generation Sunway supercomputer and its kilometer-scale application

Abstract. The global ocean general circulation model (OGCM) with kilometer-scale resolution is of great significance for understanding the climate effects of mesoscale and submesoscale eddies. To address the computational and storage demands of exponential growth associated with kilometer-scale resolution simulation for global OGCMs, we develop an enhanced and deeply optimized OGCM, namely swLICOM, on the new generation Sunway supercomputer. We design a novel split I/O scheme that effectively partitions tripole grid data across processes for reading and writing, resolving the IO bottleneck encountered in kilometer-scale resolution simulation. We also develop a new domain decomposition strategy that removes land points effectively to enhance the simulation capability. In addition, we upgrade the code translation tool swCUDA to convert the LICOM3 CUDA kernels to Sunway kernels efficiently. By further optimization using mixed precision, we achieve a peak performance of 453 Simulated Days per Day (SDPD) with 59 % parallel efficiencies at 1 km resolution, scaling up to 25 million cores. The result of simulation with a 2 km horizontal resolution shows swLICOM is capable of capturing the vigorous mesoscale eddies and active submesoscale phenomena.