dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Wed, Dec 17, 2008 at 08:13:03PM +0100, Johan Hake wrote:
> On Wednesday 17 December 2008 19:20:11 Anders Logg wrote:
> > Ola and I have now finished up the first round of getting DOLFIN to
> > run in parallel. In short, we can now parse meshes from file in
> > parallel and partition meshes in parallel (using ParMETIS).
> >
> > We reused some good ideas that Niclas Jansson had implemented in
> > PXMLMesh before, but have also made some significant changes as
> > follows:
> >
> > 1. The XML reader does not handle any partitioning.
> >
> > 2. The XML reader just reads in a chunk of the mesh data on each
> > processor (in parallel) and stores that into a LocalMeshData object
> > (one for each processor). The data is just partitioned in blocks so
> > the vertices and cells may be completely unrelated.
> >
> > 3. The partitioning takes place in MeshPartitioning::partition,
> > which gets a LocalMeshData object on each processor. It then calls
> > ParMETIS to compute a partition (in parallel) and then redistributes
> > the data accordingly. Finally, a mesh is built on each processor using
> > the local data.
> >
> > 4. All direct MPI calls (except one which should be removed) have been
> > removed from the code. Instead, we mostly rely on dolfin::MPI::distribute
> > which handles most cases of parallel communication and works with STL
> > data structures.
> >
> > 5. There is just one ParMETIS call (no initial geometric
> > partitioning). It seemed like an unnecessary step, or are there good
> > reasons to perform the partitioning in two steps?
> >
> > For testing, go to sandbox/passembly, build and then run
> >
> >   mpirun -n 4 ./demo
> >   ./plot_partitions 4
> 
> Looks beautiful!
> 
> I threw a 3D mesh of 160K vertices onto it, and it was partitioned nicely in 
> some 10 s, on my 2 core laptop.
> 
> Johan

Nice, in particular since we haven't run any 3D test cases ourselves,
just a tiny mesh of the unit square... :-)

-- 
Anders

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