On Sun, Sep 18, 2022 at 7:04 PM Barry Smith <[email protected]> wrote:
> > Right, but I want to run with the old options MIS (instead of MIS-2) and > get the same times as before. But instead I am getting much larger times. > Yea, the new MIS is noticeably slower New: petsc/src/ksp/ksp/tutorials$ mpiexec -n 4 ./ex55 -ne 511 -ksp_type cg -pc_type gamg -log_view -pc_gamg_square_graph 0 -mat_coarsen_type misk PCSetUp_GAMG+ 1 1.0 6.8526e-01 1.0 2.14e+08 1.0 1.2e+03 6.3e+03 7.3e+02 44 21 28 38 88 100100100100100 1242 GAMG Coarsen 5 1.0 5.7050e-02 1.0 0.00e+00 0.0 3.0e+02 7.1e+02 1.5e+02 4 0 7 1 18 8 0 26 3 20 0 GAMG MIS/Agg 5 1.0 5.0056e-02 1.0 0.00e+00 0.0 3.0e+02 7.1e+02 1.5e+02 3 0 7 1 18 7 0 26 3 20 0 Old: petsc/src/ksp/ksp/tutorials$ mpiexec -n 4 ./ex55 -ne 511 -ksp_type cg -pc_type gamg -log_view -pc_gamg_square_graph 0 *-mat_coarsen_type mis* ... PCSetUp_GAMG+ 1 1.0 6.7866e-01 1.0 2.14e+08 1.0 1.1e+03 7.1e+03 5.9e+02 43 21 26 39 85 100100100100100 1254 GAMG Coarsen 5 1.0 1.3564e-02 1.0 0.00e+00 0.0 1.6e+02 9.6e+02 1.5e+01 1 0 4 1 2 2 0 15 2 3 0 GAMG MIS/Agg 5 1.0 7.5110e-03 1.0 0.00e+00 0.0 1.6e+02 9.6e+02 1.5e+01 0 0 4 1 2 1 0 15 2 3 0 Same in serial: (conda_env) 05:15 adams/landau-ex13-fixes= ~/Codes/petsc/src/ksp/ksp/tutorials$ mpiexec -n 1 ./ex55 -ne 511 -ksp_type cg -pc_type gamg -log_view -pc_gamg_square_graph 0 *-mat_coarsen_type mis* | g MIS GAMG MIS/Agg 5 1.0 *3.7858e-02* 1.0 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00 1 0 0 0 0 2 0 0 0 0 0 (conda_env) 05:16 adams/landau-ex13-fixes= ~/Codes/petsc/src/ksp/ksp/tutorials$ mpiexec -n 1 ./ex55 -ne 511 -ksp_type cg -pc_type gamg -log_view -pc_gamg_square_graph 0 -mat_coarsen_type misk | g MIS GAMG MIS/Agg 5 1.0 *8.5015e-02* 1.0 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00 3 0 0 0 0 5 0 0 0 0 0 I did find that there is an unneeded MatDuplicate in MISk with just one MIS (MIS-1), but it is still slower than the old: (conda_env) 05:31 adams/landau-ex13-fixes *= ~/Codes/petsc/src/ksp/ksp/tutorials$ mpiexec -n 1 ./ex55 -ne 511 -ksp_type cg -pc_type gamg -log_view -pc_gamg_square_graph 0 -mat_coarsen_type misk | g MIS GAMG MIS/Agg 5 1.0 *5.9566e-02* 1.0 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00 2 0 0 0 0 4 0 0 0 0 0 MISk is organized differently and goes through some hoops that the old MIS does not do that are not as easy as the MatDuplicate to avoid. Mark > > On Sep 18, 2022, at 6:58 PM, Mark Adams <[email protected]> wrote: > > > > On Sun, Sep 18, 2022 at 6:19 PM Barry Smith <[email protected]> wrote: > >> >> Mark, >> >> Some how your changes to GAMG in June slowed down the time to compute >> the MIS dramatically. I cannot figure out what options to use to >> get the exact same performance as an older branch. -mat_coarsen_type mis >> -pc_gamg_threshold 0 result in longer times than the older code with its >> default options. >> > > The new MIS-2 folds in the square graph with the MIS. Before the square > graph was in a separate method that created an squared graph explicitly. > So don't use aggressive coarsening (you will see a PtAP if you use > aggressive coarsening in the new code) > And -pc_gamg_threshold 0 will filter (zeros only). Use < 0 for no > filtering. > The old code also had this optimization to not create a graph for bs==1 > and no filter, > > Mark > > >> >> >> >> On Sep 18, 2022, at 4:21 PM, Mark Adams <[email protected]> wrote: >> >> >> >> On Sun, Sep 18, 2022 at 4:02 PM Barry Smith <[email protected]> wrote: >> >>> >>> Mark, >>> >>> Do all MIS algorithms in PETSc require a symmetric graph structure? >>> And parallel ones can hang if not structurally symmetric? >>> >> >> Yes, >> >> >>> >>> When used sequentially I guess it never hangs but it may not produce >>> a "correct" MIS if the matrix structure is not symmetric? >> >> >> It is fine in serial and it is not necessarily an MIS of the >> symmetrized graph. >> If there is a one way edge between two vertices and the order of the >> greedy MIS process picks the root of the edge it is an MIS of the >> symmetrized graph, otherwise both vertices could get selected. >> >> >>> But like the MIS is fine for GAMG in this circumstance? >>> >> >> It will be fine for GAMG. The MIS is just a heuristic. >> >> >>> >>> Barry >>> >>> >> >
