Computing time per time step (open circles) as a function of the number of CPU cores. Two MPI tasks, each spawning ten OpenMP threads that are assigned to the ten cores of a CPU socket were used on each of the two-socket nodes, i.e., the total number of MPI tasks is ten times smaller than the number of CPU cores given on the abscissa. Different colors correspond to different sizes of the numerical grid. Dashed inclined lines indicate ideal strong scalability for a given grid size. Two sets of measurements in which both the number of grid points and the number of processor cores was increased by a factor of 2³ from left to right are marked by filled circles. The horizontal dotted lines are a reference for ideal weak scalability. The diamond symbols correspond to additional runs that employed a plain MPI parallelization (OpenMP switched off), i.e., the number of MPI tasks equals the number of cores.