Submitted as: development and technical paper 21 Oct 2021

Submitted as: development and technical paper | 21 Oct 2021

Review status: this preprint is currently under review for the journal GMD.

Improve Ocean Modelling Software NEMO 4.0 benchmarking and communication efficiency

Gaston Irrmann1,3, Sébastien Masson1, Éric Maisonnave2, David Guibert3, and Erwan Raffin3 Gaston Irrmann et al.
  • 1LOCEAN-IPSL, Sorbonne Universités (UPMC)/IRD/CNRS/MNHN, UMR7159, Paris, France
  • 2CERFACS/CNRS, CECI, Toulouse, France
  • 3CEPP - Center for Excellence in Performance Programming, Atos Bull, 35700 Rennes, France

Abstract. Communications in distributed memory supercomputers are still limiting scalability of geophysical models. Consid-ering the recent trends of the semiconductor industry, we think this problem is here to stay. We present the optimisations thathave been implemented in the actual 4.0 reference version of the ocean model NEMO 4.0 to improve its scalability. Thanksto the collaboration of oceanographers and HPC experts, we identified and removed the unnecessary communications in twobottleneck routines, the computation of free surface pressure gradient and the forcing in the straights or unstructured open5boundaries. Since a wrong parallel decomposition choice could undermine computing performance, we impose its automaticdefinition in all cases, including when subdomains containing land points only are excluded from the decomposition. For asmaller audience of developers and vendors, we propose a new benchmark configuration, easy to use while offering the fullcomplexity of operational versions.

Gaston Irrmann et al.

Status: open (until 16 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-320', Anonymous Referee #1, 01 Nov 2021 reply
  • RC2: 'Comment on gmd-2021-320', Anonymous Referee #2, 22 Nov 2021 reply

Gaston Irrmann et al.

Model code and software

NEMO 4.0 NEMO system team

Gaston Irrmann et al.


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Short summary
To be efficient on supercomputers, softwares must be high-performance at computing many concurrent tasks. Communications between tasks is often necessary but time consuming, ocean modelling software NEMO 4.0 is no exception. In this work we describe approaches enabling fewer communications, an optimization to share the workload more equally between tasks and a new flexible configuration to assess NEMO's performance easily.