Keeping computational performance analysis simple: an evaluation of the NEMO BENCH test

In 2019 a non-intrusive instrumentation of the NEMO code, aimed to give information about the MPI communications cost and structure of the model, was created by E. Maisonnave and S. Masson at the LOCEAN Laboratory, in Paris. The main goal was to identify which developments have to be prioritized for the model to enhance its scalability: a new NEMO configuration, called BENCH, was specifically developed for the purpose, offering some easy way to make performance measurements, and hoping to simplify future benchmark activities related to computing efficiency. 
In the first part of this work we study if this configuration can actually be used as a valid tool to get insight into NEMO’s performance, and then proceed to use the BENCH test to study some of NEMO’s most known bottlenecks: I/O and the north fold. Additionally we take the chance to investigate a topic that is gaining popularity among NEMO developers: the variability of time required to perform a timestep and how it influences NEMO’s performance, obtaining prescriptions on how to avoid or mitigate such behavior.