DILU in openfoam is our block Jacobi ilu subdomain solvers
On Tue, Jan 10, 2023, 23:45 Barry Smith wrote:
>
> The default is some kind of Jacobi plus Chebyshev, for a certain class
> of problems, it is quite good.
>
>
>
> On Jan 10, 2023, at 3:31 PM, Mark Lohry wrote:
>
> So what are people
The default is some kind of Jacobi plus Chebyshev, for a certain class of
problems, it is quite good.
> On Jan 10, 2023, at 3:31 PM, Mark Lohry 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
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 wrote:
> Mark Lohry writes:
>
> > I definitely need multigrid. I was under the impression that
Mark Lohry 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
>
> BTW, on unstructured grids, coloring requires a lot of colors and thus
> many times more bandwidth (due to multiple passes) than the operator itself.
I've noticed -- in AMGx the multicolor GS was generally dramatically slower
than jacobi because of lots of colors with few elements.
You can
The joy of GPUs. You can use sparse triangular kernels like ILU (provided by
cuBLAS), but they are so mindbogglingly slow that you'll go back to the drawing
board and try to use a multigrid method of some sort with
polynomial/point-block smoothing.
BTW, on unstructured grids, coloring requires
Well that's suboptimal. What are my options for 100% GPU solves with no
host transfers?
On Tue, Jan 10, 2023, 2:23 PM Barry Smith wrote:
>
>
> On Jan 10, 2023, at 2:19 PM, Mark Lohry wrote:
>
> Is DILU a point-block method? We have -pc_type pbjacobi (and vpbjacobi if
>> the node size is not
> On Jan 10, 2023, at 2:19 PM, Mark Lohry wrote:
>
>> Is DILU a point-block method? We have -pc_type pbjacobi (and vpbjacobi if
>> the node size is not uniform). The are good choices for scale-resolving CFD
>> on GPUs.
>
> I was hoping you'd know :) pbjacobi is underperforming ilu by a
>
> Is DILU a point-block method? We have -pc_type pbjacobi (and vpbjacobi if
> the node size is not uniform). The are good choices for scale-resolving CFD
> on GPUs.
>
I was hoping you'd know :) pbjacobi is underperforming ilu by a pretty
wide margin on some of the systems i'm looking at.
We
We don't have colored smoothers currently in PETSc.
> On Jan 10, 2023, at 12:56 PM, Jed Brown wrote:
>
> Is DILU a point-block method? We have -pc_type pbjacobi (and vpbjacobi if the
> node size is not uniform). The are good choices for scale-resolving CFD on
> GPUs.
>
> Mark Lohry
Is DILU a point-block method? We have -pc_type pbjacobi (and vpbjacobi if the
node size is not uniform). The are good choices for scale-resolving CFD on GPUs.
Mark Lohry writes:
> I'm running GAMG with CUDA, and I'm wondering how the nominally serial
> smoother algorithms are implemented on
I'm running GAMG with CUDA, and I'm wondering how the nominally serial
smoother algorithms are implemented on GPU? Specifically SOR/GS and ILU(0)
-- in e.g. AMGx these are applied by first creating a coloring, and the
smoother passes are done color by color. Is this how it's done in petsc AMG?
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