The Oasis3 MPI1/2 Parallel Version

This work describes the optimization and parallelization activities performed on the OASIS3 coupler. The test case used for evaluating and profiling the coupler consists on the CMCCMED coupled model developed by the ANS division of the CMCC and currently in production on the NEC SX9 cluster. The experiments highlighted that the most time consuming transformations are the extrapolation of the fields on the masked points (performed in the extrap function) and interpolation (performed in the scriprmp function). The optimization has been mainly focused on reducing the time spent for I/O operations this reduced the coupling time of 27%. The parallelization of the OASIS3 has been a further step for reducing the elapsed time of the whole coupled model. The proposed parallel approach is based on the distribution of the fields among the available processes. Each process is in charge to apply the coupling transformations on the assigned fields. With this approach the number of coupling fields represents an upper bound to the parallelization level. However this approach can be fully combined with the parallelization based on the geographical domain distribution. The work concludes with a qualitative comparison of the proposed approach with the OASIS3 pseudoparallel version developed by CERFACS.