[Pw_forum] Parallelization of diaghg

[Axel Kohlmeyer]

On 1/6/07, Alexander Shaposhnikov <shaposh at isp.nsc.ru> wrote:
> Hi,
>
> yet another parallelization issue. As far as i understand, subroutine  cdiaghg
> for davidson diagonalization  is not parallelized
> by default (in recent versions) and this is for good, as enabling parallel
> algorithm ('david + para ') only increases computation time (almost always for
> me).
> Profiling shows this routine takes 1/2 -2/3 exec times for big  jobs running
> in parallel on 8-core dual Xeon clovertown 2.66GHz machine, so some working
> parallelization algorithm could give sizeable performance boost.

well, on the other hand you have to consider the problem of memory
contention, which must be a huge problem on a machine like yours.

i suggest, you first do a test by starting a series of 1, 2, 3,
4,...,8 identical
and not too small serial calculations simultaneously and compare the wall
time of those jobs to get an impression of how much of a performance
improvement from this kind of machine is maximally possible (this is
an ideally parallel problem with no communication). i have not previous
experience with that kind of hardware, but extrapolating from woodcrest
performance numbers and the fact, that your cpus are for all practical
purposes two woodcrest cpus glued on one socket, i'd expect that you'd
see a significant performance degradation when running 8 processes.
i would not be surprised if the optimum would be to use only two thirds
or even half the cores for larger problems.

cheers,
    axel.
>
> I'd like to hear any comments from respected developers concerning this issue.
>
> Best Regards,
> Alexander Shaposhnikov
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>


-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
  Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
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