dolfin team mailing list archive

[Johan Hake <hake@xxxxxxxxx>]

On Wednesday 17 December 2008 20:19:52 Anders Logg wrote:
> 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... :-)

Yes I thought so too ;) 

Johan