[Pw_forum] default parallelization and parallelization of bands.x

[Maxim Skripnik]

Thank you for the information. Yes, at the beginning of the pw.x output it says:
     Parallel version (MPI), running on    64 processors
     R & G space division:  proc/nbgrp/npool/nimage =      64

Is bands.x parallelized at all? If so, where can I find information on that? There's nothing mentioned in the documentation:
http://www.quantum-espresso.org/wp-content/uploads/Doc/pp_user_guide.pdf
http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_BANDS.html

What could be the reason for bands.x taking many hours to calculate the bands? The foregoing pw.x calculation has already determined the energy for each k-point along a path (Gamma -> K -> M -> Gamma). There are 61 k-points and 129 bands. So what is bands.x actaully doing beside reformating that data? The input file job.bands looks like this:
 &bands
    prefix   = 'st1'
    outdir   = './tmp'
/
The calculation is initiated by
mpirun -np 64 bands.x < job.bands

Maxim Skripnik
Department of Physics
University of Konstanz

Am Samstag, 05. Dezember 2015 02:37 CET, stefano de gironcoli <degironc at sissa.it> schrieb:
  On 04/12/2015 22:53, Maxim Skripnik wrote:Hello,

I'm a bit confused by the parallelization scheme of QE. First of all, I run calculations on a cluster with usually 1 to 8 nodes, each of which has 16 cores. There is a very good scaling of pw.x e.g. for structural relaxation jobs. I do not specify any particular parallelization scheme as mentioned in the documentation, i.e. I start the calculations with
mpirun -np 128 pw.x < job.pw
on 8 nodes, 16 cores each. According to the documentation ni=1, nk=1 and nt=1. So in which respect are the calculations parallelized by default? Why do the calculations scale so well without specifying ni, nk, nt, nd?R and G parallelization is performed.
wavefunctions' planewaves, density planewaves and slices of real space objects are distributed across 128 processors. A report of how this is done is given at the beginning of the output.
Did you had a look to it ?
 Second question is, whether one can speed up bands.x calculations. Up to now I start these this way:
mpirun -np 64 bands.x < job.bands
on 4 nodes, 16 cores each. Does it make sense to define nb for bands.x? If yes, what would be reasonable values? expect no gain. band parallelization is not implemented in bands.

stefano






 The systems of interest consist of typically ~50 atoms with periodic boundaries.

Maxim Skripnik
Department of Physics
University of Konstanz  _______________________________________________
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