[Pw_forum] default parallelization and parallelization of bands.x

[stefano de gironcoli]

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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