[petsc-users] MatCreateSeqAIJWithArrays for GPU / cusparse

[Mark Lohry]

You have my condolences if you have to support all those things
simultaneously.

On Wed, Jan 4, 2023, 7:27 PM Matthew Knepley <knepley at gmail.com> wrote:

> On Wed, Jan 4, 2023 at 7:22 PM Junchao Zhang <junchao.zhang at gmail.com>
> wrote:
>
>> We don't have a machine for us to test with both "--with-cuda --with-hip"
>>
>
> Yes, but your answer suggested that the structure of the code prevented
> this combination.
>
>   Thanks,
>
>      Matt
>
>
>> --Junchao Zhang
>>
>>
>> On Wed, Jan 4, 2023 at 6:17 PM Matthew Knepley <knepley at gmail.com> wrote:
>>
>>> On Wed, Jan 4, 2023 at 7:09 PM Junchao Zhang <junchao.zhang at gmail.com>
>>> wrote:
>>>
>>>> On Wed, Jan 4, 2023 at 6:02 PM Matthew Knepley <knepley at gmail.com>
>>>> wrote:
>>>>
>>>>> 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.
>>>>>
>>>> We define either PETSC_HAVE_CUDA or PETSC_HAVE_HIP or NONE, but not
>>>> both
>>>>
>>>
>>> Where is the logic for that in the code? This seems like a crazy design.
>>>
>>>   Thanks,
>>>
>>>     Matt
>>>
>>>
>>>>   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/>
>>>>>
>>>>
>>>
>>> --
>>> 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/>
>>>
>>
>
> --
> 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/>
>
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