Matt you were right I was stupidly passing the wrong array (column major order) to Metis. My code is in Fortran. I am surprised Metis didnt crash before.
Thanks anyway. Tabrez On 08/25/2011 11:49 PM, Matthew Knepley wrote: > On Thu, Aug 25, 2011 at 9:15 PM, Tabrez Ali <stali at geology.wisc.edu > <mailto: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 > > 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/20110826/81a9c330/attachment.htm>
