[petsc-users] MatCreateSeqAIJWithArrays for GPU / cusparse

[Mark Lohry]

>
> Maybe we could add a MatCreateSeqAIJCUSPARSEWithArrays(), but then we
> would need another for MATMPIAIJCUSPARSE, and then for HIPSPARSE on AMD
> GPUs, ...


Wouldn't one function suffice? Assuming these are contiguous arrays in CSR
format, they're just raw device pointers in all cases.

On Wed, Jan 4, 2023 at 6:02 PM Junchao Zhang <junchao.zhang at gmail.com>
wrote:

> No, we don't have a counterpart of MatCreateSeqAIJWithArrays() for GPUs.
> Maybe we could add a MatCreateSeqAIJCUSPARSEWithArrays(), but then we would
> need another for MATMPIAIJCUSPARSE, and then for HIPSPARSE on AMD GPUs, ...
>
> The real problem I think is to deal with multiple MPI ranks. Providing the
> split arrays for petsc MATMPIAIJ is not easy and thus is discouraged for
> users to do so.
>
> A workaround is to let petsc build the matrix and allocate the memory,
> then you call MatSeqAIJCUSPARSEGetArray() to get the array and fill it up.
>
> We recently added routines to support matrix assembly on GPUs, see if
> MatSetValuesCOO
> <https://petsc.org/release/docs/manualpages/Mat/MatSetValuesCOO/> helps
>
> --Junchao Zhang
>
>
> On Wed, Jan 4, 2023 at 2:22 PM Mark Lohry <mlohry at gmail.com> wrote:
>
>> I have a sparse matrix constructed in non-petsc code using a standard CSR
>> representation where I compute the Jacobian to be used in an implicit TS
>> context. In the CPU world I call
>>
>> MatCreateSeqAIJWithArrays(PETSC_COMM_WORLD, nrows, ncols, rowidxptr,
>> colidxptr, valptr, Jac);
>>
>> which as I understand it -- (1) never copies/allocates that information,
>> and the matrix Jac is just a non-owning view into the already allocated
>> CSR, (2) I can write directly into the original data structures and the Mat
>> just "knows" about it, although it still needs a call to
>> MatAssemblyBegin/MatAssemblyEnd after modifying the values. So far this
>> works great with GAMG.
>>
>> I have the same CSR representation filled in GPU data allocated with
>> cudaMalloc and filled on-device. Is there an equivalent Mat constructor for
>> GPU arrays, or some other way to avoid unnecessary copies?
>>
>> Thanks,
>> Mark
>>
>
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