dolfin team mailing list archive

[Matthew Knepley <knepley@xxxxxxxxx>]

On Mon, Sep 21, 2009 at 2:51 PM, Garth N. Wells <gnw20@xxxxxxxxx> wrote:

>
>
> Matthew Knepley wrote:
>
>> On Mon, Sep 21, 2009 at 2:37 PM, Anders Logg <logg@xxxxxxxxx <mailto:
>> 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.
>>
>>
> Isn't this only for a Krylov solver? The demo uses MUMPS.
>

MUMPS should not even scale as well as a matvec.

  Matt


> Garth
>
>
>  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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>>
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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
>>
>>
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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