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

[Matthew Knepley]

On Mon, Oct 31, 2011 at 4:29 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Oct 31, 2011, at 11:14 AM, Matthew Knepley wrote:
>
> > 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.
>
>    Maybe you should change the manual page to make this whole business
> clear. Currently one could interpret it in a variety of ways.
>
>   For example "Inserts many blocks of values into a matrix at once."
> "Inserts" isn't really right
>
>   and "In the future, we may extend this routine to handle rectangular
> blocks, and additive mode."   What the hey is "additive mode"? I thought
> ADD_VALUES as opposed to INSERT_VALUES.
>
>    and just say that it cannot be called multiply times before
> MatAssemblyBegin/End ....


Done.

   Matt


>
>    Barry
>
> >
> >    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
>
>


-- 
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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