dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 27 September 2011 03:55, Johan Hake <johan.hake@xxxxxxxxx> wrote:
> On Monday September 26 2011 16:52:02 Johan Hake wrote:
>> Hello!
>>
>> I played around with the OpenMP assembler as I really needed to speed up
>> some assemble because of problems with Real Spaces. Speedwise it looked
>> really promissing, untill I compared the results...
>>
>> It turns out that the result is not correct for forms with Real spaces
>> included. Anyone knows why and if there is an easy fix?
>>
>>   https://bugs.launchpad.net/dolfin/+bug/860142
>>
>> I would really like to fix this one ASAP...
>
> The easiest is probably for me to flesh out the forms with no global dofs in
> and pass these to the OpenMP assembler.
>
> To fix this more permanently we need to collect the rows and columns of the
> global dofs in separate vectors. After the assemble we can add them separtely.
>
> To make it thread safe we can first sum the vectors over the threads and then
> add them outside the openmp loop. I think this strategi might speed up
> insertion into PETSc Matrices for forms with global dofs too.
>

I added something to a Blueprint recently. PETSc 3.2 has a new
function that assembles everything at once. What we need to add in
DOLFIN is an 'unassmebled matrix' backend that stores each local
matrix block. It could be a good solution to issue that is described.

> For this to be robust and fast we need to make ufc global dof aware. Maybe
> extend ufc dof_map with:
>
>  tabulate_global_dofs(double* dofs);
>  num_global_dofs();
>

This can be done already, in a way. Have a look at

  DofMapBuilder::compute_global_dofs

It can figure out the global dof indices.

> What you say before or after the 1.0 release ;)
>

Sounds desperate. My money is on after.

Garth

> Johan
>
>> I also discovered that OpenMP assemble crashes for scalars. This is not as
>> critical as scalars are pretty fast to assemble anyhow.
>>
>>   https://bugs.launchpad.net/dolfin/+bug/860040
>>
>> Johan
>>
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