mpb-mpi speedup vs. serial mpb

hi everyone,

i was wondering if i could get some advice from folks familiar with  
the parallel version of MPB about mpb-mpi's performance.

i have built mpb-mpi on a cluster running Scientific Linux 3.0; the  
various packages i am using are:

fftw-2.1.5   hdf5-1.6.5    libctl-3.0.2  openmpi-1.1.2
guile-1.8.1  lapack-3.1.0  mpb-1.4.2

i have also built a serial version of MPB on the same cluster, using  
the same packages, but without MPI support.

i am doing some initial check-out of the two builds using the  
diamond.ctl file from the MPB manual.  both builds give results  
consistent with the manual, but i am concerned about the amount of  
time each takes to complete:

- the serial mpb takes 66 seconds to complete (on the head node, which  
is identical to the compute nodes)
- mpb-mpi takes 75 seconds to complete, using 1 processor
- mpb-mpi takes 61 seconds to complete, using 2 processors
- mpb-mpi takes 57 seconds to complete, using 4 processors

which is pretty bad linearity with respect to the number of processors  
involved. however this is also a pretty small job.  is this normal for  
mpb-mpi calculations involving small jobs?  can i expect an  
improvement with larger jobs, or should i dig into locally-specific  
issues like interconnects or scheduling priorities and whatnot?

thanks!
-nate

(by the way, Steven:  this version of guile is complaining about  
deprecated function calls, which i don't mind, but thought you might  
like to know about:

scm_must_malloc is deprecated.  Use scm_gc_malloc and scm_gc_free instead.

)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
nate lipkowitz
416 823 8057
[email protected]