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We report our experiences in implementing a set of modifications to the NEMO ocean modelling code intended to improve the code's performance and scalability on HECToR and other large multi-core scalar systems. These modifications were inspired by the coastal ocean modelling code POLCOMS, and involved re-ordering 3-dimensional array indices and associated loop nests, multi-core aware partitioning, and elimination of redundant computation on land. The modifications are invasive, pervasive and mutually dependent, and we under-estimated the effort required to implement them fully in NEMO. We report performance results from our partial implementation, and provide revised estimates of the effort required to complete a full implementation and the likely performance benefits. We also describe by-products of this work that have been incorporated in the production use of NEMO, including dynamic memory allocation, various bug fixes, and a solution to an issue degrading NEMO's performance on HECToR. |
