Hello,
I have a simple AMR code using SerialMesh. I run it 70 refinements on 12
cores. In metis_partitioner.C, I print out the partition result as follows.
437 // Otherwise use kway
438 else
439 Metis::METIS_PartGraphKway(&n, &ncon, &csr_graph.offsets[0],
&csr_graph.vals[0], &vwgt[0], NULL,
440 NULL, &nparts, NULL, NULL, NULL,
441 &edgecut, &part[0]);
442
443 for (int i = 0; i < mesh.n_processors(); i++) { // my code
444 int cnt = 0;
445 for (int j = 0; j < n; j++) if (part[j] == i) cnt++;
446 printf("METIS assigned %d elements to proc %d\n", cnt, i);
447 }
I found in the last few iterations, the partition result is severely
imbalanced. For example, in last iteration, proc 11 has 9M+ elements, while
others only have hundreds or thousands.
METIS assigned 2829 elements to proc 0
METIS assigned 270 elements to proc 1
METIS assigned 804 elements to proc 2
METIS assigned 264 elements to proc 3
METIS assigned 263 elements to proc 4
METIS assigned 733 elements to proc 5
METIS assigned 273 elements to proc 6
METIS assigned 407 elements to proc 7
METIS assigned 1200 elements to proc 8
METIS assigned 4795 elements to proc 9
METIS assigned 23404 elements to proc 10
METIS assigned 9866034 elements to proc 11
My mesh has only triangles, with at most one hanging node. I did not assign
any weight to nodes and I found libMesh uses number of nodes as weight (in
my case, it should be 3). I tried to changed &vwgt[0] to NULL when calling
METIS. From the printf, I got a quite balanced partitioning. However, the
program execution time increased a lot.
Any clues?
Thank you!
--Junchao Zhang
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