real space grid decomposition

Noam Bernstein no... at
Fri Apr 22 20:47:49 UTC 2011

Am I correct in surmising that real space grids are decomposed over nodes only
along the 1st dimension?

I'm reaching a parallelization bottleneck for QM/MM.  If I do atom
based parallelization,
I get pw_restrict_s3 and corresponding routines that take a lot of
time and don't
speed up.  If I do grid based parallelization I get no speedup once
the number of
parallel processes is comparable to the size of the 1st dimension of the real
space grid (-18..18 = 39 in my case).  With 32 processes I get some
but poor load balance, because some processes do grid x value and some do 2.
For 64 processes some processes are actually doing no work in
qmmm_forces_with_gaussian_LG(), for example

Is there anything I'm missing?


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