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

[Cesar Hernandez]

Hi

I see the same behaviour using Pentium 4 Quad-Core (5 machines). I've
tested mpich v1, lammpi and openmpi. Using 8 or more cores the
performance is very poor, and the total time of procesing increases
quickly....
Do you mean the problem is the memory bandwidth? That's it, the latency
of the RAM bus?

Cesar

El jue, 02-10-2008 a las 18:20 -0700, Erick van Rijk escribió:
> 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/
> >
> 
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-- 
Cesar Hernandez
chernandez at genos.es
Genos Open Source S.L.