Gridding and Load Balancing

Nyx has a great deal of flexibility when it comes to how to decompose the computational domain into individual rectangular grids, and how to distribute those grids to MPI ranks. There can be grids of different sizes, more than one grid per MPI rank, and different strategies for distributing the grids to MPI ranks.

We use the phrase “load balancing” here to refer to the combined process of grid creation (and re-creation when regridding) and distribution of grids to MPI ranks.

See Grid Creation for grids are created, i.e. how the BoxArray on which MultiFabs will be built is defined at each level.

See Load Balancing for the strategies AMReX supports for distributing grids to MPI ranks, i.e. defining the DistributionMapping with which MultiFabs at that level will be built.

When running on multicore machines with OpenMP, we can also control the distribution of work by setting the size of grid tiles (by defining fabarray_mfiter.tile_size). We can also specify the strategy for assigning tiles to OpenMP threads. See the AMReX documentation for more about tiling.

• Grid Creation
• Load Balancing
• Load Balancing the Hydrodynamical Mesh
• Load Balancing the Dark Matter Particles