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

[Erick van Rijk]

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 and the  
efficiency is dropping off rapidly
The efficiency goes from 87% for 2 cores to 64% for 4 cores and down  
to 53% for 8 cores.
Some other testing done by R. Fovell (http://macwrf.blogspot.com/2008/03/wrfv221-on-dual-quad-mac-pro.html 
) shows similar behaviour.
Although there is about 4% overhead caused by barriers/communication  
running with 8 threads, I don't really see why there is such a  
significant performance degradation.
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).

Thank you,

Erick