[Pw_forum] question on parallelism options and scaling factor

[pascal boulet]

Dear all,

I have a basic question about parallelism and scaling factor.

First, I am running calculations on a cubic system with 58 atoms
(alat=19.5652  a.u.), 540 electrons (324 KS states) and few k-points
(4x4x4 grid=4 k-points), on 32 cores (4 nodes) but I can submit on many
more.

I guess the best thing to do is to parallelize the calculation on the
bands but maybe also on the FFTs. We have an infiniband interconnection
network between the nodes.

What would you suggest as values for image/pools/ntg/bands ?

I have made a SCF test calculation on 16 and 32 cores. For the SCF cycle
(13 steps) I get the following timing:
For 16 cores: total cpu time spent up to now is    22362.4 secs
For 32 cores: total cpu time spent up to now is    17932.6 secs

The speedup is "only" 25%. I would have expected a better speedup for
such a small number of cores. Am i wrong? What is your experience?

(For additional information, if helpful: QE 5.0.1 has been compiled with
openMPI, intel 12.1 and FFTW 3.2.2.)

thank you for your answers.

Regards
Pascal

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