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

[Kevin Matthew Nuss]

Hi Anders,

The "OMP_NUM_THREADS=4" needs to be set pryor to running the program rather
than before compiling. That environmental variable from the shell is checked
implicitly at the beginning of each run. I have used it on my Linux
workstation in the past. I imagine the newer releases will work just fine
too, although I have not tried it with any "ideal" simulations.

Kevin



On Wed, Sep 7, 2011 at 3:44 PM, Anders A Nottrott <anottrot at ucsd.edu> wrote:

> 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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>
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