[Wrf-users] Benchmarking problems

[Craig Tierney]

On 3/14/11 1:08 PM, Bart Brashers wrote:
> I'm trying to benchmark WRF on two comparable systems, Intel X5660 and
> AMD 6174, before I buy.  I'm also trying to do a benchmark for those of
> us who have many 5-day WRF runs to complete -- many runs with relatively
> low core counts, rather than a single run with large core counts (the
> focus of most benchmarks).
>
> I downloaded the WRF 3.0 Benchmark parts from
> http://www.mmm.ucar.edu/wrf/WG2/bench/.  I compiled using option 2
> (smpar for PGI/gcc) with no problems.  In the namelist.input I specified
> (for one particular run):
>
> &domains
> ...snip...
>   numtiles                            = 1,
>   nproc_x                             = 3,
>   nproc_y                             = 2,
>   num_metgrid_levels                  = 40,
> /
>
> I set OMP_NUM_THREADS to 6 in my run script that calls wrf.exe.
>
> And yet, when I look in the resulting wrf.out file I see:
>
>   WRF NUMBER OF TILES FROM OMP_GET_MAX_THREADS =   6
>   WRF NUMBER OF TILES =   6
>
> Hey! I told you to use 1 tile and split it 3 by 2!
>
> Is this a problem with WRF v3.0?  Looking at some WRF 3.2.1 runs where I
> have numtiles = 1 and specified 4 by 1, I got more verbose output like "
> WRF TILE   1 IS      1 IE    165 JS      1 JE     33".
>
> Scaling is poor after only 4 cores, so I suspect something is going
> wrong.  Any suggestions you have would be greatly appreciated.
>

I am not sure about the split, but I do know that at low core core counts
you are going to get better performance using MPI, even if you are only
using a single node.

If you are using OpenMP, you need to look into issues related to
socket-affinity to ensure that your OpenMP threads stay local to the
socket.  If you don't get the affinity right, it is going to hurt scalability.

Craig




> Bart
>
>
>
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