Performance study of a parallel domain decomposition method

N. Odry (1) , J.-F. Vidal (1) , G. Rimpault (1) , J.-J. Lautard (1) , A.-M. Baudron (1)

1 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)

This paper studies the influence of various parameters, in order to improve the performances of a parallel Domain Decomposition Method ($aka$ DDM). If introducing more parallelism represents an opportunity to heighten the performance of deterministic schemes, substantial modifications of their architecture are required. In this context, DDM has been implemented into the Apollo3 multigroup $S_n$ solver, Minaret. The fundamental idea involves splitting a large boundary value problem into several $independent$ subproblems, that can be computed in parallel.Two $DDM$ algorithms are considered. The first one solves a one-group problem per subdomain. The second one is a multigroup block-Jacobi algorithm. To improve performances of these DDM,various parallelism strategies are implemented and compared, depending on the internal structure of the DDM algorithm, the technology chosen (MPI or OpenMP), and the variable parallelized (angular direction or subdomain). Based on these considerations, an efficient $hybrid$ parallelism,suitable for $HPC$ is built a parallel multigroup Jacobi iteration algorithm, using a two layerMPI/OpenMP architecture, gives the best performances for the reactor configuration studied.

Mots clés: domain decomposition; parallel computing; Apollo3

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique Nucléaire Théorique [nucl-th]

N. Odry, J.-F. Vidal, G. Rimpault, J.-J. Lautard, A.-M. Baudron. Performance study of a parallel domain decomposition method. PHYSOR 2016 - International Conference on the Physics of Reactors: Unifying Theory and Experiments in the 21st Century, May 2016, Sun Valley, United States. ⟨hal-02442270⟩