Hi Freddie,

Thanks for the pointers.

Profiling showed that the MPI communication was actually the bottleneck. 
Apparently, the communication was going through the (very slow) ethernet 
port by default and therefore slowing down the simulation overall. After 
specifying the correct interface - Infiniband - the simulation got about 
5-6 times faster. MPI time fell back to a reasonable 15%, mostly waiting 
for Isend/Irecv to complete.

I've started simulating the same geometry but with the compressible 
formulation, as it runs much faster. I ran the case (input file attached) 
with a series of combination of MPI ranks (from 1 per core to 1 per CPU) 
and OpenMP threads. I found that this had essentially no effect on the wall 
time, even though the MPI comm time increases with the number of MPI ranks 
(from 11% to 32%).

Thanks,

Solal


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