Thanks Stefano and Chonglin! DILU in openfoam is our block Jacobi ilu subdomain solvers >
are you saying that -pc_type gang -mg_levels_pc_type -mg_levels_ksp_type richardson gives you something exactly equivalent to DILU? On Tue, Jan 10, 2023 at 4:04 PM Zhang, Chonglin <[email protected]> wrote: > I am using the following in my Poisson solver running on GPU, which were > suggested by Barry and Mark (Dr. Mark Adams). > -ksp_type cg > -pc_type gamg > -mg_levels_ksp_type chebyshev > -mg_levels_pc_type jacobi > > > On Jan 10, 2023, at 3:31 PM, Mark Lohry <[email protected]> wrote: > > So what are people using for GAMG configs on GPU? I was hoping petsc today > would be performance competitive with AMGx but it sounds like that's not > the case? > > On Tue, Jan 10, 2023 at 3:03 PM Jed Brown <[email protected]> wrote: > >> Mark Lohry <[email protected]> writes: >> >> > I definitely need multigrid. I was under the impression that GAMG was >> > relatively cuda-complete, is that not the case? What functionality works >> > fully on GPU and what doesn't, without any host transfers (aside from >> > what's needed for MPI)? >> > >> > If I use -ksp-pc_type gamg -mg_levels_pc_type pbjacobi >> -mg_levels_ksp_type >> > richardson is that fully on device, but -mg_levels_pc_type ilu or >> > -mg_levels_pc_type sor require transfers? >> >> You can do `-mg_levels_pc_type ilu`, but it'll be extremely slow (like >> 20x slower than an operator apply). One can use Krylov smoothers, though >> that's more synchronization. Automatic construction of operator-dependent >> multistage smoothers for linear multigrid (because Chebyshev only works for >> problems that have eigenvalues near the real axis) is something I've wanted >> to develop for at least a decade, but time is always short. I might put >> some effort into p-MG with such smoothers this year as we add DDES to our >> scale-resolving compressible solver. >> > >
