ffc team mailing list archive

[Kristian Ølgaard <k.b.oelgaard@xxxxxxxxx>]

On 2 August 2010 15:45, Florian Rathgeber
<florian.rathgeber@xxxxxxxxxxxxxx> wrote:
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> Hi,
>
> I modified FFC to accept an additional option for the -l parameter to
> output tensor tabulation code suitable for execution in a CUDA kernel on
> the GPU. For that the indexing for coordinates, coefficients and the
> element tensor needs to be changed since the data structures look
> differently on the GPU (foremost they are flattened). The Jacobi
> computations look differently as well due to the way coordinates are stored.
>
> What I did was to provide a function override_gpu() in cpp.py that
> updates the cpp.format dictionary to generate the correct index into the
> data structures. This function is called at the beginning of
> codegeneration.py:generate_code if the GPU target was specified by the
> - -l parameter.
>
> This works for tensor representation, but not functions values
> (including coefficients) for quadrature, since the corresponding code is
> generated by the class "QuadratureTransformerBase". I'm no Python
> expert, but I assume the override of cpp.format on the global scope is
> not visible inside the class scope.

It will be if you call override_gpu() in the representation stage
instead of the code generation stage.

> Since "QuadratureTransformerBase" does not get the parameters, it cannot
> know if the target is GPU and override_gpu() should be called.
>
> My changes are more of a quick hack and certainly not a well-designed
> way to solve this. I would be happy about suggestions both to quickly
> fix the quadrature and also how to adapt the whole design to make it
> more "clean" and straightforward.

We handle the formatting of floats in a similar way so I don't think
the solution is too bad for now.

> (The corresponding wrapper code, which is different from the ordinary
> DOLFIN wrapper code, is also generated depending on the -l option, but
> that is a different topic, so I just mention it for the sake of
> completeness)

and the option is '-l dolfin-gpu' if anyone wonders.

Kristian

> I published my branch here:
> https://code.launchpad.net/~florian-rathgeber/ffc/gpu-wrappers
>
> Florian
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