[petsc-users] Ghost point communication for Red-Black Gauss-Siedel

[Sylvain Barbot]

> R-B has crappy cache performance since you alternately pull data but ignore
> half of it.

Understood.

> Why not just use the GMG in PETSc? Its very flexible, scalable,
> and efficient.

I tried to use Petsc's implementation of multigrid, cf thread "V-cycle
multigrid with matrix shells". My concern is performance. I'd like the
whole procedure to use matrix shells, or "matrix-free" matrices,
because my stencil can have up to 21 off-diagonal terms. Petsc 3.1 did
not allow this functionality. I do not know what Petsc 3.2 has to
offer in that regard.

I have a working multi-grid method that uses the low functionality of
Petsc. I would obviously prefer if I could use something more
advanced.

Cheers,
Sylvain