[Wrf-users] How to limit number of threads in 'smpar' OpenMP runs?

[Anders A Nottrott]

Hi All,

 

I am trying to run an ideal LES simulation as a parallel process (i.e. using
option 'smpar'). I have an 8 core machine but I would like to limit the
number of threads to 4. I tried setting the environment variable
'OMP_NUM_THREADS=4' prior to configuration and compilation. However, when I
run wrf.exe I get the following just before the simulation begins:

WRF NUMBER OF TILES FROM OMP_GET_MAX_THREADS = 8
WRF TILE 1 IS 1 IE 100 JS 1 JE 13
WRF TILE 2 IS 1 IE 100 JS 14 JE 26
WRF TILE 3 IS 1 IE 100 JS 27 JE 38
WRF TILE 4 IS 1 IE 100 JS 39 JE 50
WRF TILE 5 IS 1 IE 100 JS 51 JE 62
WRF TILE 6 IS 1 IE 100 JS 63 JE 74
WRF TILE 7 IS 1 IE 100 JS 75 JE 87
WRF TILE 8 IS 1 IE 100 JS 88 JE 100
WRF NUMBER OF TILES = 8

I looked in 'module_tiles.F' and it appears that the variable 'num_tiles' is
assigned by the OMP_GET_MAX_THREADS function. Perhaps this is overriding the
environment setting??? Note that when I check my system performance the code
is running on all 8 cores, but this is not efficient since I want to run
other process on my machine. 

 

I also messed with some of the parameters in the namelist, e.g. 'tile_sz_x',
'tile_sz_y', 'numtiles', 'nproc_x', 'nproc_y', but to no avail.

 

Any suggestions will be most appreciated.

 

Regards,

 

Anders

 

 

Anders Nottrott

PhD Student, Mechanical and Environmental Engineering

University of California, San Diego

Department of Mechanical and Aerospace Engineering

Website: <solar.ucsd.edu/nottrott>

 

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