dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Fri, Aug 29, 2008 at 08:57:17AM +0200, Niclas Jansson wrote:
> Anders Logg wrote:
> 
> >>>>> Where do we start?
> >>>>>
> >>>>> I guess one good place to start would be to get input/partitioning
> >>>>> working and you seem to have that working already. We should be able
> >>>>> to read in a mesh, partition it (with ParMetis for now) and construct
> >>>>> the MeshFunctions S_i and F_i.
> >>>>>
> >>>>> Once that is in place, we can start hacking on DofMapBuilder::build().
> >>>>>
> >>>>> Could you outline what you have in terms of input/partitioning and
> >>>>> then we can start applying those patches.
> >>>>>
> >>>> Parallel mesh parsing, the entire mesh is never represented on a single
> >>>> processor. It's a two stage process, first the coordinates are loaded
> >>>> and partitioned with a geometric partitioner. In the second stage each
> >>>> processor loads the cells corresponding to the assigned coordinates, and
> >>>> finally the mesh is partitioned with a graph partitioner.
> >>>>
> >>>> Partitioning is done with the distributed geometric and mesh-to-dual
> >>>> graph partitioner in parmetis.
> >>> How does this work? It seems as if you have already partitioned the
> >>> domain geometrically, then there's no need to make a partition based on
> >>> topology. Or is the geometric partitioning only a first approximation
> >>> and then vertices are exchanged between processors?
> >>>
> >>
> >> The coordinates in the XML-file are initially distributed across the
> >> processors with a simple linear distribution, just to get it of the hard
> >> drive.
> >>
> >> The geometric partitioner is used to make sure that all coordinates on a
> >> processor lies close to each other. This simplifies and minimize
> >> communication when parsing cell data.
> >>
> >> Since the geometric partitioner creates rather bad partitions (with
> >> respected to edge-cut), the graph partitioner is used to create a good
> >> partitioning, with low edge-cut, thus minimizing
> >> data-dependencies/communication.
> > 
> > Sounds good. Can you submit this in one or more patches, starting with
> > the parallel XML parser?
> > 
> 
> Yes, I could at least split it into two or three patches.
> 
> 
> Niclas

Nice!

-- 
Anders

Attachment: signature.asc
Description: Digital signature