[petsc-users] speedup for TS solver using DMDA

[Matthew Knepley]

On Mon, Sep 15, 2014 at 12:45 PM, Katy Ghantous <katyghantous at gmail.com>
wrote:

> Hi,
> I am using DMDA to run in parallel TS to solves a set of N equations. I am
> using DMDAGetCorners in the RHSfunction with setting the stencil size at 2
> to solve a set of coupled ODEs on 30 cores.
> The machine has 32 cores (2 physical CPUs with 2x8 core each with speed of
> 3.4Ghz per core).
> However, mpiexec with more than one core is showing no speedup.
> Also at the configuring/testing stage for petsc on that machine, there was
> no speedup and it only reported one node.
> Is there somehting wrong with how i configured petsc or is the approach
> inappropriate for the machine?
> I am not sure what files (or sections of the code) you would need to be
> able to answer my question.
>

The kind of code you describe sounds memory bandwidth limited. More
information is here:

  http://www.mcs.anl.gov/petsc/documentation/faq.html#computers

The STREAMS should give you an idea of the bandwidth, and running it on 2
procs vs 1 should
give you an idea of the speedup to expect, no matter how many cores you use.

  Thanks,

     Matt


> Thank you!
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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