Mark Lohry <mlo...@gmail.com> 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.
