[petsc-dev] Backend independent VecGetArray for GPUs

[Karl Rupp]

Hi Ashwin,

I pushed a function for obtaining the CUDA pointer from a CUSP vector here:
https://bitbucket.org/petsc/petsc/commits/d831094ec27070ea54a249045841367f8aab0976

It currently resides in branch
  karlrupp/feature-gpu-handle-access-for-vec

The respective function for ViennaCL will be pushed later.
Please let me know if this works for you, then I'll start the 
integration process.

Best regards,
Karli


On 10/19/2014 04:12 PM, Ashwin Srinath wrote:
> Thanks Karl!
>
> Ashwin
>
> On Sun, Oct 19, 2014 at 9:45 AM, Karl Rupp <rupp at iue.tuwien.ac.at
> <mailto:rupp at iue.tuwien.ac.at>> wrote:
>
>     Hi Ashwin,
>
>     I'll add two functions returning the bare CUDA and OpenCL handles.
>
>     Best regards,
>     Karli
>
>
>     On 10/19/2014 03:42 PM, Ashwin Srinath wrote:
>
>         Hi everyone
>
>         Just wondering what the consensus is. I'm happy to submit a PR if
>         someone can tell me what goes where!
>
>         Thanks
>         Ashwin
>
>         On 18 Oct 2014 01:46, "Karl Rupp" <rupp at iue.tuwien.ac.at
>         <mailto:rupp at iue.tuwien.ac.at>
>         <mailto:rupp at iue.tuwien.ac.at <mailto:rupp at iue.tuwien.ac.at>>__>
>         wrote:
>
>              Hi,
>
>               >> > Why would we want this? The packages themselves
>              (CUDA/ViennaCL) only
>
>                      expose
>                      memory using these specific types. What use is it
>         to wrap
>                      these up in
>                      a void * if you
>                      just have to caste back down to use them. Isn't it
>         better to
>                      maintain
>                      type-specific, and
>                      type safe, interfaces for this stuff?
>
>                      The biggest problem I faced was that there was no
>         way to
>                      access device
>                      memory using petsc4py - since there is no
>         equivalent for
>                      VecCUSPGetArray. So returning a raw pointer may not
>         be very
>                      helpful
>                      for C++/CUSP users (they already have a nice way to
>         access
>                      device
>                      memory) but it would definitely make things a lot
>         easier for
>                      Python users.
>
>
>                  To me it sounds like something that should be dealt
>         with in the
>                  library
>                  that does the python bindings, not in PETSc itself. (...)
>
>
>              Unfortunately, this is not so easy: If the Python wrapper
>         has to
>              take care of such a conversion, then it needs to use the
>         *exactly
>              same build environment* as PETSc. The reason is that the
>         CUSP and
>              ViennaCL types are C++ beasts, not having a defined ABI, so
>         one can
>              run into all sorts of hard-to-debug problems when finally
>         linking
>              libpetsc.so with the Python wrapper. If, however, PETSc
>         provides
>              these low-level memory buffers, the Python wrapper can
>         attach to a
>              well-defined ABI.
>
>              Best regards,
>              Karli
>
>
>