[mpas-developers] Block Decomposition Revision

[Doug Jacobsen]

Hi again all,

I have attached a newer updated version of the design doc, with several
changes related to discussions I have had with various people. The changes
should also address a lot of the concerns that were presented in previous
emails about this topic.

I have also included some bigger picture information and general timeline
information for the whole project ( all of tasks 1 through 5, not just this
one).

Please let me know if you have any questions or concerns regarding this
newly updated document.

Doug

On Thu, Jan 26, 2012 at 11:01 AM, Michael Duda <duda at ucar.edu> wrote:

> Hi, Doug.
>
> Thanks very much for the document. I'm still thinking through the design
> section, but I have a couple of quick comments on the requirements.
> First, I think we need to be careful about including implementation
> details in the requirements themselves. For example, the requirement
>
>   "Domain decomposition information needs to be read from a file based on
>    number of total blocks as opposed to number of MPI tasks."
>
> says quite a bit about how this should be implemented ("needs to be read
> from a file"). Secondly, even though the initial design may take the
> simplest approach to assigning multiple blocks to a task, I think it
> will be good to ensure that the requirements describe our long-term
> requirements for the module.
>
> Two of the requirements could be something along the lines of:
>
> 1) the user must be able to specify the number of blocks to be owned by
>   each task; and
>
> 2) the block_decomp module must return information describing the cells
>   contained in the specified number of blocks for the task.
>
> As for additional requirements, we could consider whether it is the case
> that we ultimately want to be able to specify a different number of
> blocks for each MPI task, and if we want to be able to place additional
> constraints on which blocks are assigned to a task (much harder, I
> think; e.g., preference should be given for contiguously located blocks
> to maximize shared-memory copies, or for blocks that are spread as
> evenly around the global domain as possible to help with load balancing).
>
> I apologize for taking so long to have a look through the document; I'll
> send along any other comments that might come up as soon as I can.
>
> Regards,
> Michael
>
>
> On Tue, Jan 24, 2012 at 01:26:53PM -0700, Doug Jacobsen wrote:
> > Hi All,
> >
> > Continuing with the work that Michale previously proposed before the
> > derived data type revision, I am starting work on revisions to the block
> > decomposition module to support multiple blocks per mpi process. As a
> > refresher, this item was previously described as
> >
> > 4) Modify the block_decomp module to enable a task to get a list of
> >     cells in more than one block that it is to be the owner of.
> >     Implemented in the simplest way, there could simply be a namelist
> >     option to specify how many blocks each task should own, and the
> >     block_decomp module could look for a graph.info.part.n file, with
> >     n=num_blocks_per_task*num_tasks, and assign blocks k, 2k, 3k, ...,
> >     num_blocks_per_task*k to task k.
> >
> > I have attached a design document (pdf and latex) related to this task.
> > Please let me know if you have any comments or suggestions. I would like
> to
> > have this implemented by the end of the week. Thanks for any feedback.
> >
> > Doug
>
>
>
> > _______________________________________________
> > mpas-developers mailing list
> > mpas-developers at mailman.ucar.edu
> > http://mailman.ucar.edu/mailman/listinfo/mpas-developers
>
>
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