On Thu, Aug 25, 2011 at 9:15 PM, Tabrez Ali <stali at geology.wisc.edu> wrote:
> Hello > > I have an unstructured FE mesh which I am partitioning using Metis. > > In the first case I only use the element partitioning info and discard the > nodal partitioning info i.e., the original ordering is same as petsc's > global ordering. In the second case I do use the nodal partitioning info and > nodes are distributed accordingly. > > I would expect that in the 2nd scenario the total number of MPI messages > (at the end of the solve) would be lower than the 1st. However I see that > opposite is true. See the plot at > http://stali.freeshell.org/**mpi.png<http://stali.freeshell.org/mpi.png> > > The number on the y axis is the last column of the "MPI messages:" field > from the -log_summary output. > > Any ideas as to why this is happening. Does relying on total number of MPI > messages as a performance measure even make sense. Please excuse my > ignorance on the subject. > > Alternatively what is a good way to measure how good the Metis partitioning > is? > The thing to do here is take a case like 2 proc that can be completely understood, and get down to the details. I think there is a probably just a simple misunderstanding here. The first thing to check is that you are partitioning what you think. By default, Metis partitions the vertices of a graph, not elements, Thus you usually have to give Metis the "dual" of your finite element mesh. I would take a small (maybe 8 or 10 elements) mesh and look at the original and Metis partitions. If Metis does not look better, something is wrong. Matt > Thanks in advance > > Tabrez > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20110826/ed79ba52/attachment.htm>
