[petsc-users] GPU implementation of serial smoothers

[Mark Lohry]

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 <bsmith at petsc.dev> wrote:

>
>
> On Jan 10, 2023, at 2:19 PM, Mark Lohry <mlohry at gmail.com> 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 pretty
> wide margin on some of the systems i'm looking at.
>
> We don't have colored smoothers currently in PETSc.
>>
>
> So what happens under the hood when I run -mg_levels_pc_type sor on GPU?
> Are you actually decomposing the matrix into lower and computing updates
> with matrix multiplications? Or is it just the standard serial algorithm
> with thread safety ignored?
>
>
>   It is running the regular SOR on the CPU and needs to copy up the vector
> and copy down the result.
>
>
> On Tue, Jan 10, 2023 at 1:52 PM Barry Smith <bsmith at petsc.dev> wrote:
>
>>
>>   We don't have colored smoothers currently in PETSc.
>>
>> > On Jan 10, 2023, at 12:56 PM, Jed Brown <jed at jedbrown.org> 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 <mlohry at gmail.com> writes:
>> >
>> >> 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?
>> >>
>> >> Tangential, AMGx and OpenFOAM offer something called "DILU", diagonal
>> ILU.
>> >> Is there an equivalent in petsc?
>> >>
>> >> Thanks,
>> >> Mark
>>
>>
>
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