Use MPI_Dist_graph_create to determine comm pattern#1358
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Tested it on Frontier. Need to test it more thoroughly:
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aprokop
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Rombur
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May 18, 2026
| dest_weights[i] = _dest_offsets[i + 1] - _dest_offsets[i]; | ||
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| MPI_Comm graph_comm; | ||
| MPI_Dist_graph_create(_comm, (outdegree ? 1 : 0), &comm_rank, &outdegree, |
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Can we save the graph or do we need to rebuild it every time?
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Right now, we don't use it past Distributor construction. I do want to try to use it for neighborhood communications inside doPostsAndWaits in the future. I'll store it then if it works out.
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MPI_Alltoallhas issues with scaling. This patch replaces it by usingMPI_Dist_graph_createand other helper functions to rely on MPI. This seems to scale better on Frontier:This bumps our MPI requirement to 2.2.