Sure, but have you ever seen such a large jump in time in going from one to two MPI ranks, and are there any algorithms to do the aggregation that would not require this very expensive parallel symmetrization?
> On Sep 17, 2022, at 9:07 AM, Mark Adams <mfad...@lbl.gov> wrote: > > Symetrix graph make a transpose and then adds them. > I imagine adding two different matrices is expensive. > > On Fri, Sep 16, 2022 at 8:30 PM Barry Smith <bsm...@petsc.dev > <mailto:bsm...@petsc.dev>> wrote: > > Mark, > > I have runs of GAMG on one and two ranks with -pc_gamg_symmetrize_graph > because the matrix is far from symmetric and some of GAMG is taking a huge > amount more time with 2 ranks than one. (While other stuff like VecNorm shows > improvement with two ranks). I've attached the two files > > Have you seen this before, is there anything that can be done about? If > going to two ranks causes almost a doubling in GAMG setup time that makes > using parallelism not useful, > > Barry >
