Analysis of a New MPI Process Distribution for the Weather Research and Forecasting (WRF) Model

Algorithm 1

Integration step (solve_em) pseudocode obtained from WRF Fortran code.

(1)	function COMPUTE_SOMETHING(tile)
(2)	for to do         Iterate the tile
(3)	for to do      The iteration order is OK
(4)	for to do
(5)	tile[i][k][j] = …      Do something on the grid
(6)	end for
(7)	end for
(8)	end for
(9)	end function
(10)	procedure SOLVE_EM(subdomain)
(11)	…                      Initialization
(12)	!$OMP PARALLEL DO             One thread per tile
(13)	for to numtiles do           Iterate tiles
(14)	compute_something(subdomain[t])    Pass the tile to the function to compute something
(15)	end for
(16)	!$OMP END PARALLEL DO       End of parallel region
(17)	if DM_PARALLEL then          If MPI is being used
(18)	HALO_EM∗∗∗.inc    Send halos to other adjacent processes depending on the stencil
(19)	end if
(20)	…   Replicate the same loop structure tens of times for the different variables to compute on the subdomain
(21)	end procedure