Re: [Starpu-devel] StarPU Fortran support

[Olivier Aumage <olivier.aumage@inria.fr>]

Dear Matthias,

There are two ways to use StarPU for a Fortran application:


** Using the Native Fortran API:

You can have a look at examples in the STARPU/examples/native_fortran/ 
directory. 
For instance, to use a CUDA kernel with the example nf_vector.f90, you can 
replace
the following lines:
%-------------------
        ! add a CPU implementation function to the codelet
        call fstarpu_codelet_add_cpu_func(cl_vec, C_FUNLOC(cl_cpu_func_vec))
%-------------------

with:
%-------------------
        ! add a CUDA implementation function to the codelet
        call fstarpu_codelet_add_cuda_func(cl_vec, C_FUNLOC(... CUDA kernel 
launch function ...))
%-------------------

and replace every remaining occurrence of cpu/CPU with cuda/CUDA.


If you want to use both CPU dans CUDA kernels for the same codelet, you can 
remove the call to fstarpu_codelet_set_where() and add both kernels to the 
same codelet:
%-------------------
        call fstarpu_codelet_add_cpu_func(cl_vec, C_FUNLOC(cl_cpu_func_vec))
        call fstarpu_codelet_add_cuda_func(cl_vec, C_FUNLOC(... CUDA kernel 
launch function ...))
%-------------------


** Using C marshaling functions:

The example in the STARPU/examples/fortran90/ directory uses the C marshaling 
approach, where all interactions between the Fortran application with StarPU 
(both the application calls to StarPU and the StarPU calls to application 
kernels) are done through a custom C layer. Here, the use of CUDA kernels is 
exactly the same as for a C/C++ application.


The native Fortran API of StarPU is more convenient, but it requires a 
Fortran compiler compliant with ISO/IEC TS 29113:2012 
(see https://www.iso.org/standard/45136.html). You can try to build the
examples in StarPU/Examples/native_fortran to check if your compiler is ok.
Recent versions of GNU GFortran and Intel Fortran compilers are known to
build these examples successfully.

The C marshaling way works with any Fortran compiler supporting 
'iso_c_binding',
but it requires more coding.

Best regards,
-- 
Olivier Aumage
Inria Researcher
Team STORM

> Le 1 nov. 2017 à 10:09, Matthias Lieber <matthias.lieber@tu-dresden.de> a 
> écrit :
> 
> Dear StarPU developers,
> 
> I am interested in trying out StarPU for a Fortran application.
> However, the documentation and the examples do not show how to
> specify accelerator kernels for codelets. So my quesion is:
> Does the Fortran interface support GPUs (preferably CUDA) and
> how is done?
> 
> Best wishes
> Matthias
> 
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