[QE-users] Advice for Parallel Execution

[Robert Fleming]

Greetings,

I’m running scf calculations on an amorphous Si surface terminated with different functional groups (input file attached for context), and I’m experiencing poor scaling behavior in parallel.  I’m running these jobs locally on an 8-core CPU to test before scaling up the system size to an hpc cluster.

I’ve noticed that increasing the number of MPI processes from 4 to 8 (mpirun -n 4 pw.x -in [myscript] vs. mpirun -n 8 pw.x -in [myscript]) results in the job taking longer (~ 1hr vs. 1.5 hr).  Looking through the documentation, I see that there are several command line switches for different levels of parallelization beyond just the number of MPI processes.  While it’s possible that my system size is potentially too small to benefit from parallel execution (24 atoms, 103 electrons), I think it’s probably more likely that I’m not appropriately taking advantage of these.

Would anyone be willing to share some advice or “rules of thumb” on the best way to select these parallelization levels for small-to-medium sized jobs (say, an 8 core CPU vs. 150-200 processors on an hpc platform)?

Thank you,
________________________________
Robert “Drew” Fleming, Ph.D.
Assistant Professor of Mechanical Engineering
College of Engineering & Computer Science
Arkansas State University
(870) 972-3743
rofleming at AState.edu<mailto:rofleming at AState.edu>






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