[gmx-users] Is the PME domain decomposition flexible in some hidden way?

[Paolo Franz]

Thank you very much for the help. I read the part of the manual you
referred to, it is now clear how to choose the decomposition.
Cheers
Paolo

On 3 April 2012 17:16, Mark Abraham <Mark.Abraham at anu.edu.au> wrote:

> On 3/04/2012 11:58 PM, Paolo Franz wrote:
>
>> Hello!
>> I am wondering if the domain decomposition chosen by the code, once the
>> number of cpus dedicated to PME is chosen,can be overridden somehow. That
>> is, if in some sort there exist a reciprocal space equivalent of "-dd" for
>> the domain decomposition of the direct space. The problem I have is that I
>> am trying to get a good scaling factor for some large system I have, on
>> 1000/2000 CPUs. If for instance I have 128 CPU on PME and a 128^3 grid, I
>> would like to have a decomposition 8X16X1 on PME, which should be perfectly
>> ok with the parallelization scheme, if I understand it correctly.
>> Unfortunately, the default one I get is 128X1X1, which is inevitably very
>> inefficient. Is there anything I could be doing?
>>
>
> The automatic choice depends on a large number of factors. A big factor is
> optimizing the PP<->PME communication load. Big common factors in the
> divisions of processors into grids are key, so long as those factors can
> lead to useful hardware mappings. In particular, see last para 3.17.5 of
> manual.
>
> Mark
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