Efficient CFD code implementation for the ARM-based Mont-Blanc architecture

This paper is devoted to the optimizations carried out in the TermoFluids CFD code to efficiently run it on the Mont-Blanc system. The underlying numerical method is based on an unstructured finite-volume discretization of the Navier-Stokes equations for the numerical simulation of incompressible turbulent flows. It is implemented using a portable and modular operational approach based on a minimal set of linear algebra operations. An architecture-specific heterogeneous multilevel MPI+OpenMP+OpenCL implementation of such kernels is proposed. It includes optimizations of the storage formats, dynamic load balancing between the CPU and GPU devices and hiding of communication overheads by overlapping computations and data transfers. A detailed performance study shows time reductions of up to 2.1× on the kernels' execution with the new heterogeneous implementation, its scalability on up to 128 Mont-Blanc nodes and the energy savings (around 40%) achieved with the Mont-Blanc system versus the high-end hybrid supercomputer MinoTauro.