[Wrf-users] Poor scalability of WRFV221 on 8-core machine

[Erick van Rijk]

My reasoning for using OMP is that my test machine is a single unit  
MPI will only harm in that scenario.
The overhead of launching separate processes, duplicating the dataset  
for every instance, is considerable and with omp the communication  
latency is lower than MPI.

I agree that the available bandwidth per core declines if you add more  
cores to share the same bus, but I expected that 2 Intel Xeon 5400  
processors could handle that.

Erick
On Oct 2, 2008, at 5:59 PM, Gerardo Cisneros wrote:

> On Thu, 2 Oct 2008, Erick van Rijk wrote:
>
>> Hello everybody,
>> I have been looking into the scalability of WRFV221 on my 8-core
>> machine and I have noticed that the scalability is very poor [...]
>>
>> Do any of the user/developers want to comment on this? Any reason why
>> this is happening or point me to somewhere that can cause this
>> behaviour?
>> I have build wrf221 with ifort and openmp enabled (not using MPI).
>
> (a)  WRF scaling with OpenMP only isn't anywhere
> near what can be obtained by using MPI.
>
> (b)  Memory bandwidth per core dwindles as you
> use more cores in your shared-memory machine.
>
> Saludos,
>
> Gerardo
> -- 
> Dr. Gerardo Cisneros	|SGI (Silicon Graphics, S.A. de C.V.)
> Scientist             	|Av. Vasco de Quiroga 3000, Col. Santa Fe
> gerardo at sgi.com		|01210 Mexico, D.F., MEXICO
> (+52-55)5563-7958 	|http://www.sgi.com/
>