dolfin team mailing list archive

[Matthew Knepley <knepley@xxxxxxxxx>]

On Mon, Sep 21, 2009 at 2:37 PM, Anders Logg <logg@xxxxxxxxx> wrote:

> Johan and I have set up a benchmark for parallel speedup in
>
>  bench/fem/speedup
>
> Here are some preliminary results:
>
>  Speedup  |  Assemble  Assemble + solve
>  --------------------------------------
>  1        |         1                 1
>  2        |    1.4351            4.0785
>  4        |    2.3763            6.9076
>  8        |    3.7458            9.4648
>  16       |    6.3143            19.369
>  32       |    7.6207            33.699
>

These numbers are very very strange for a number of reasons:

1) Assemble should scale almost perfectly. Something is wrong here.

2) Solve should scale like a matvec, which should not be this good,
    especially on a cluster with a slow network. I would expect 85% or so.

3) If any of these are dual core, then it really does not make sense since
    it should be bandwidth limited.

  Matt


> These numbers look a bit strange, especially the superlinear speedup
> for assemble + solve. There might be a bug somewhere in the benchmark
> code.
>
> Anyway, we have some preliminary results that at least show some kind
> of speedup.
>
> It would be interesting to hear some comments on what kind of numbers
> we should expect to get from Matt and others.
>
> The benchmark is for assembling and solving Poisson on a 64 x 64 x 64
> mesh using PETSc/MUMPS. Partitioning time is not included in the
> numbers.
>
> --
> Anders
>
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-- 
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