Experience on the parallelization of the OASIS3 coupler

This work describes the optimization and paralleliza- tion of the OASIS3 coupler. Performance evaluation and profiling have been carried out by means of the CMCC-MED coupled model, developed at the Euro- Mediterranean Centre for Climate Change (CMCC) and currently running on a NEC SX9 cluster. Our experiments highlighted that extrapolation (accom- plished by the extrap function) and interpolation (im- plemented from the scriprmp function) transforma- tions take the most time. Optimization concerned I/O operations reducing coupling time by 27%. Paral- lelization of OASIS3 represents a further step towards overall improvement of the whole coupled model. Our proposed parallel approach distributes fields over a pool of available processes. Each process applies cou- pling transformations to its assigned fields. This ap- proach restricts parallelization level to the number of coupling fields. However, it can be fully combined with a parallelization approach considering the geo- graphical domain distribution. Finally a quantitative comparison of the parallel coupler with the OASIS3 pseudo-parallel version is proposed.