[Pw_forum] PW taskgroups and a large run on a BG/P

[David Farrell]

I think this summary is about right. At least I can run something now  
and have an idea of what it is. I will probably also be transitioning  
to cp for my runs.

I have been working with the folks at the supercomputing center, and  
will continue in hopes of finding out what is causing the trouble.

Thanks,

Dave

On Feb 13, 2009, at 3:33 AM, Paolo Giannozzi wrote:

> In conclusion, and if I understand correctly:
>
>  PWscf runs only with 1 MPI process per core, but
>  it runs 800+ atoms in as little as 32 processes
>  or in as much as 512, as I was expecting.
>
> This confirms my opinion that the problem is on the
> BG side and not on the PWscf side, since there is
> NOTHING in the fortran code that depends upon where
> the MPI processes are running. Of course one can
> never rule out the possibility that some obscure
> bug is triggered only in that special cases, but
> it seems to me highly unlikely.
>
> Implementation of mixed MPI-openMPI parallelization
> is under development, but it wil take some time. In
> the meantime, if you can link openMPI-aware
> mathematical libraries, you might get some speedup.
>
> If you do not need k-points, and if you know how to
> deal with metallic systems, you might try CP instead
> of PWscf - it is better tested for large systems - but
> I don't expect a different behavior, since the routines
> performing parallel subspace diagonalization are the
> same that perform iterative orthonormalization, so the
> trouble is likely to move from "cholesky" to "ortho".
>
> You might try to find out what is wrong, since you have
> two cases that should yield exactly the same results
> but don't. It may take a lot of time and lead to no
> result, though. You may also try to raise this issue
> with the technical staff of the computing center.
>
> Paolo
> -- 
> Paolo Giannozzi, Democritos and University of Udine, Italy

David E. Farrell
Post-Doctoral Fellow
Department of Materials Science and Engineering
Northwestern University
email: d-farrell2 at northwestern.edu

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