[petsc-users] Questions about setting values for GPU based matrices

[Fredrik Heffer Valdmanis]

2011/10/30 Matthew Knepley <knepley at gmail.com>

> On Sun, Oct 30, 2011 at 12:22 PM, Fredrik Heffer Valdmanis <
> fredva at ifi.uio.no> wrote:
>
>> 2011/10/28 Matthew Knepley <knepley at gmail.com>
>>
>>> On Fri, Oct 28, 2011 at 10:24 AM, Fredrik Heffer Valdmanis <
>>> fredva at ifi.uio.no> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am working on integrating the new GPU based vectors and matrices into
>>>> FEniCS. Now, I'm looking at the possibility for getting some speedup during
>>>> finite element assembly, specifically when inserting the local element
>>>> matrix into the global element matrix. In that regard, I have a few
>>>> questions I hope you can help me out with:
>>>>
>>>> - When calling MatSetValues with a MATSEQAIJCUSP matrix as parameter,
>>>> what exactly is it that happens? As far as I can see, MatSetValues is not
>>>> implemented for GPU based matrices, neither is the mat->ops->setvalues set
>>>> to point at any function for this Mat type.
>>>>
>>>
>>> Yes, MatSetValues always operates on the CPU side. It would not make
>>> sense to do individual operations on the GPU.
>>>
>>> I have written batched of assembly for element matrices that are all the
>>> same size:
>>>
>>>
>>> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatSetValuesBatch.html
>>>
>>
>> Thanks. I assume that the best way to use the batch function is to batch
>> up all element matrices and insert all with one function call? Or is it
>> recommended to split it up into several smaller batches?
>>
>
> Right now, several batches does not work.For insertion to be efficient,
> you should keep the matrices in COO
> format, or convert them back. We do not do either right now. The idea is
> to see if it ever matters for applications.
>
>
> OK, thanks.

Any estimate on when additive mode will be added to MatSetValuesBatch? As
it is now, this batch function is of limited use to us, as it forces us to
maintain an extra internal data structure to handle accumulation of numbers
that are inserted at the same indices in the matrix.

Any particular reason you chose not to support additive mode in this first
implementation? Are there any considerations I should be aware of?

Thanks,

Fredrik
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