[Pw_forum] Parallelization

[vijaya subramanian]

Thanks for your reply. I had started an earlier thread under the same heading and 
you had replied-no other reason for using your name only. I should have continued it but it was a
few weeks old.

> From: paolo.giannozzi at uniud.it
> To: pw_forum at pwscf.org
> Date: Wed, 12 Jun 2013 18:30:23 +0200
> Subject: Re: [Pw_forum] Parallelization
> 
> On Tue, 2013-06-11 at 19:57 +0000, vijaya subramanian wrote:
> 
> > Hi Paolo
> 
> you know, there are 1605 subscribed user on the pw_forum mailing list.
> Even if part of them are actually disabled, it is a lot of people. 
> Why do you address to me?
> 
> Your unit cells are quite large, your cutoff is not small, and you
> use spin-orbit, a feature that increases the memory footprint and 
> is less optimized than "plain-vanilla" calculations. In order to 
> run such large jobs, one needs to know quite a bit about the
> inner working of parallelization, which arrays are distributed,
> which are not ... The following arrays, for instance:
> 
> >         Each <psi_i|beta_j> matrix    350.63 Mb     (   5440, 2, 2112)
> 
> are not distributed. This is the kind of arrays that causes bottlenecks.
> If you have N mpi processes per node, you have N such arrays filling
> the same physical memory. Reducing the number of MPI processes per node
> and using OpenMP instead might be a good strategy.
> 
> P.
> -- 
>  Paolo Giannozzi, Dept. Chemistry&Physics&Environment, 
>  Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
>  Phone +39-0432-558216, fax +39-0432-558222 
> 
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