The size of the blocks for which the domain is
is set by two parameters in the domain_size module
(contained in the file domain_size.F90 in the run
directory). The parameter
block_size_x determines the number of physical
grid points in the first horizontal dimension; the
parameter block_size_y determines the number
of physical grid points in the (wait for it...) second
horizontal dimension. The two parameters
max_blocks_tropic determine the maximum number
of blocks that can be distributed onto a processor or node.
An initial guess for these two parameters can be made
by dividing the total number of blocks by the number
of processors you plan to run on
As mentioned in previous sections, finding the optimal block size and distribution can require experimentation. However, a starting point for users who are familiar with previous versions of POP is to set the block size such that only one block is distributed on each processor. In this case, block_size_x = nx_global/NPROCX where NPROCX is the value found in the old POP .gnu files; values for the y direction are computed analogously. The max_blocks parameters are then set to one. After using this configuration, users can experiment with reducing the block size to improve performance.
-DBLCKX=$BLCKX -DBLCKY=$BLCKY -DMXBLCKS=$MXBLCKS