[petsc-users] Using CPR with PETSC and GPU

[Junchao Zhang]

Add petsc-users.

On Tue, Jun 16, 2026 at 8:14 AM Barry Smith <bsmith at petsc.dev> wrote:

>
>     PCFIELDSPLIT should be utilizing the GPU though it may take some
> tinkering to get everything on the GPU. First what GPU are using using
> NVIDIA? And MatType of MATAIJCUSPARSE?
>
>     PCFIELDSPLIT uses MatCreateSubMatrix() to create the parts of the
> matrix needed for the subsolve.
>
>     If you are comfortable with a debugger the easiest way to track what
> is going on is run with one MPI process in the debugger
> (-start_in_debugger) and watch what kind of vectors and matrices (CPU or
> GPU) are created especially in PCSetUp_FieldSplit().
>
>    Barry
>
>   Side note to PETSc developers. Are there/could there be better ways to
> make it easier to track the GPU usage of objects in a complicated run?
>
> On Jun 16, 2026, at 12:00 AM, Junchao Zhang <junchao.zhang at gmail.com>
> wrote:
>
> Barry,  how does petsc handle a matrix in fieldsplit?  Will it extract
> entries on the host?
>
> --Junchao Zhang
>
> On Fri, Jun 12, 2026 at 5:04 PM Renato E Poli <rpoli at utexas.edu> wrote:
>
>> Hi
>>
>> We are trying to use a CPR preconditioner for a multiphase flow solver
>> using the fieldsplit option. It seems to work. We see a reduced number of
>> iterations.
>> However, it is not using the GPU effectively.
>>
>> Is there any documentation that could help?
>> Is the fieldsplit+GPU supported? (v. 3.25.2)
>>
>> These are the options we are using (after a bit of trial-and-error):
>>
>> -ksp_type fgmres
>> -ksp_gmres_restart 40
>> -pc_fieldsplit_type multiplicative
>> -fieldsplit_pressure_ksp_type preonly
>> -fieldsplit_pressure_pc_type hypre
>> -fieldsplit_pressure_pc_hypre_type boomeramg
>> -fieldsplit_other_ksp_type gmres
>> -fieldsplit_other_ksp_gmres_restart 5
>> -fieldsplit_other_ksp_max_it 5
>> -fieldsplit_other_ksp_rtol 1e-1
>> -fieldsplit_other_pc_type bjacobi
>> -fieldsplit_other_sub_pc_type ilu
>> -fieldsplit_other_sub_pc_factor_reuse_ordering true
>> -fieldsplit_other_sub_pc_factor_reuse_fill true
>>
>> Thank you,
>> Renato
>>
>
>
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