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

[Matthew Knepley]

On Mon, Oct 31, 2011 at 3:54 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>  Matt,
>
>    Won't you always want ADD_VALUES support? After all this is how finite
> element matrix assembly is done. Each element stiffness becomes one block
> in the batch and then they get added into the global matrix? How would one
> use the current batch routine with finite elements?


Of course ADD_VALUES works. What does not work is calling it multiple times
on the same matrix, for the reasons I stated.

   Matt


>
>    Barry
>
> On Oct 31, 2011, at 10:48 AM, Matthew Knepley wrote:
>
> > On Mon, Oct 31, 2011 at 12:31 PM, Fredrik Heffer Valdmanis <
> fredva at ifi.uio.no> wrote:
> > 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.
> >
> > I cannot understand what you need this for. All you need is the complete
> list of element matrices.
> >
> > Any particular reason you chose not to support additive mode in this
> first implementation? Are there any considerations I should be aware of?
> >
> > I said why above. It would require data structure changes and code
> support, and we would need some level of user request for that.
> >
> >    Matt
> >
> > Thanks,
> >
> > Fredrik
> >
> >
> >
> >
> > --
> > 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
>
>


-- 
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
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