[petsc-users] MatCreateSeqAIJWithArrays for GPU / cusparse

[Matthew Knepley]

On Wed, Jan 4, 2023 at 6:49 PM Junchao Zhang <junchao.zhang at gmail.com>
wrote:

>
> On Wed, Jan 4, 2023 at 5:40 PM Mark Lohry <mlohry at gmail.com> wrote:
>
>> Oh, is the device backend not known at compile time?
>>
> Currently it is known at compile time.
>

Are you sure? I don't think it is known at compile time.

  Thanks,

     Matt


> Or multiple backends can be alive at once?
>>
>
> Some petsc developers (Jed and Barry) want to support this, but we are
> incapable now.
>
>
>>
>> On Wed, Jan 4, 2023, 6:27 PM Junchao Zhang <junchao.zhang at gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Wed, Jan 4, 2023 at 5:19 PM Mark Lohry <mlohry at gmail.com> wrote:
>>>
>>>> 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.
>>>>
>>> But we need to know what device it is (to dispatch to either petsc-CUDA
>>> or petsc-HIP backend)
>>>
>>>
>>>>
>>>> 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
>>>>>>
>>>>>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20230104/67880547/attachment.html>