[petsc-users] [GPU] Jacobi preconditioner

[Barry Smith]

  I thought the CUPM code was intended to allow us to have common code between NVIDIA and AMD?


> On Jul 31, 2025, at 11:05 AM, Junchao Zhang <junchao.zhang at gmail.com> wrote:
> 
> What would embarrass me more is to copy the same code to MatGetDiagonal_SeqAIJHIPSPARSE.
> 
> --Junchao Zhang
> 
> On Wed, Jul 30, 2025 at 1:34 PM Barry Smith <bsmith at petsc.dev <mailto:bsmith at petsc.dev>> wrote:
>> 
>>    We absolutely should have a MatGetDiagonal_SeqAIJCUSPARSE(). It's somewhat embarrassing that we don't provide this.
>> 
>>    I have found some potential code at https://urldefense.us/v3/__https://stackoverflow.com/questions/60311408/how-to-get-the-diagonal-of-a-sparse-matrix-in-cusparse__;!!G_uCfscf7eWS!eLhrliC3tod70b6fK9DQP7SuUvKtsIneNpgXgVdXLWFXMXRsKAfGlg0YEjNrjJFgq5MlEJNOJYyHZwCl9AoymJ4$ 
>> 
>>    Barry
>> 
>> 
>> 
>> 
>>> On Jul 28, 2025, at 11:43 AM, Junchao Zhang <junchao.zhang at gmail.com <mailto:junchao.zhang at gmail.com>> wrote:
>>> 
>>> Yes, MatGetDiagonal_SeqAIJCUSPARSE hasn't been implemented.  petsc/cuda and petsc/kokkos backends are separate code.  
>>> If petsc/kokkos meet your needs, then just use them.  For petsc users, we hope it will be just a difference of extra --download-kokkos --download-kokkos-kernels in configuration. 
>>> 
>>> --Junchao Zhang
>>> 
>>> 
>>> On Mon, Jul 28, 2025 at 2:51 AM LEDAC Pierre <Pierre.LEDAC at cea.fr <mailto:Pierre.LEDAC at cea.fr>> wrote:
>>>> Hello all,
>>>> 
>>>> 
>>>> 
>>>> We are solving with PETSc a linear system updated every time step (constant stencil but coefficients changing).
>>>> 
>>>> 
>>>> 
>>>> The matrix is preallocated once with MatSetPreallocationCOO() then filled each time step with MatSetValuesCOO() and we use device pointers for coo_i, coo_j, and coefficients values.
>>>> 
>>>> 
>>>> 
>>>> It is working fine with a GMRES Ksp solver and PC Jacobi but we are surprised to see that every time step, during PCSetUp, MatGetDiagonal_SeqAIJ is called whereas the matrix is on the device. Looking at the API, it seems there is no MatGetDiagonal_SeqAIJCUSPARSE() but a MatGetDiagonal_SeqAIJKOKKOS().
>>>> 
>>>> 
>>>> 
>>>> Does it mean we should use Kokkos backend in PETSc to have Jacobi preconditioner built directly on device ? Or I am doing something wrong ?
>>>> 
>>>> NB: Gmres is running well on device.
>>>> 
>>>> 
>>>> 
>>>> I could use -ksp_reuse_preconditioner to avoid Jacobi being recreated each solve on host but it increases significantly the number of iterations.
>>>> 
>>>> 
>>>> 
>>>> Thanks,
>>>> 
>>>> 
>>>> 
>>>> <pastedImage.png>
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> Pierre LEDAC
>>>> Commissariat à l’énergie atomique et aux énergies alternatives
>>>> Centre de SACLAY
>>>> DES/ISAS/DM2S/SGLS/LCAN
>>>> Bâtiment 451 – point courrier n°41
>>>> F-91191 Gif-sur-Yvette
>>>> +33 1 69 08 04 03
>>>> +33 6 83 42 05 79
>> 

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