<p><strong>Abstract</strong></p>
<p>The developments realised in OASIS3‐MCT to improve its parallel efficiency are detailed. These will be available in the next release OASIS3‐MCT_4.0 planned for spring 2018. The most important improvements concern the communication scheme and the hybrid MPI+OpenMP parallelisation of theSpherical Coordinate Remapping and Interpolation Package (SCRIP) library. The new communication method, which can now use the mapping weights to define the intermediate mapping decomposition, takes longer to initialise but offers significant gain at run time, especially for high‐resolution cases running on a high number of tasks. The parallelisation introduced in the SCRIP library for the mapping weight calculation allows a reduction in the weight calculation time of 2 to 3 orders of magnitude for high‐resolution grids. Also, significant gains are obtained in the initialisation phase by updating the MCT library from version 2.8 to 2.10.beta1 and additional debugging. New methods introduced in the CONSERV post‐processing operation ensuring the global conservation of the coupling fields lower the calculation costs by one order of magnitude while still ensuring good level of reproducibility. Finally, additional results obtained with IS‐ENES2 coupling technology benchmarks show that OASIS3‐MCT performs as well as, and even better at very high number of cores, than other coupling technologies and<br>
that its behaviour on Marconi KNL is fully satisfactory.</p>
<p><strong>About this document</strong></p>
<ul>
<li>Work package in charge: WP2 Scalability</li>
<li>Actual delivery date for this deliverable: 28 March 2018</li>
<li>Dissemination level: PU (for public use)</li>
<li>Lead author: Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS): Sophie Valcke</li>
<li>Other contributing authors: Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS): Laure Coquart, Anthony Craig, Gabriel Jonville, Eric Maisonnave, Andrea Piacentini</li>
<li>Internal reviewers: Sveriges Meteorologiska och Hydrologiska Institut (SMHI): Uwe Fladrich, BULL/ATOS (BULL): David Guibert, Erwan Raffin, Deutsches Klimarechenzentrum (DKRZ): Philipp Neumann</li>
</ul
