[QE-users] parallelization of pw.x

[Michal Krompiec]

Dear Pietro, dear Giuseppe,
Thanks, indeed my comment on speedup was hasty and didn’t make sense.
Thanks for the suggestions regarding increasing number of mpi processes and
not using nt.
Best,
Michal

On Thu, 30 May 2019 at 16:18, Pietro Delugas <pdelugas at sissa.it> wrote:

> Dear Michal
>
> 3.7x with respect to what ?
>
> your cut and paste refers to the wall time and the total cpu time per mpi
> task, they differ because you are using thread parallelism.
>
> if you don't have memory issues I would try to increase the number of mpi
> processes decreasing the number of thread and usually when the number on
> MPI tasks is smaller than the dimesions of the fft grid it is better to
> avoid using nt.
>
> Hope it helps
>
> regards
>
> Pietro
> On 30/05/19 16:42, Michal Krompiec wrote:
>
> Hello,
> I am trying to run a calculation on a 2D slab with a bit of adsorbate (119
> atoms in total), and I would like to parallelize it as much as possible. I
> am using a 3 3 1 Monkhorst-Pack grid (so I have 5 k-points).
> I tried using -npool 5 -nt 4 using 20 MPI processes and 5 threads per
> process but, as it seems, the speedup was just 3.7x:
>    PWSCF        :   1d 4h27m CPU      7h43m WALL
> What could have gone wrong, is there anything "obvious" I can do to
> diagnose the problem? I am using QE 6.4rc, compiled with gcc and OpenMPI,
> without ELPA.
>
> Best regards,
>
> Michal Krompiec
>
> Merck KGaA and University of Southampton
>
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