[CP2K:1765] Re: GPGPU status

[Ondrej Marsalek]

Hi again,

thanks a lot to everyone who commented (and stayed on topic).

Let me please review "out loud" what I have understood the current
situation to be.

1) CUDA/GPGPU for the whole of CP2K (and therefore I assume any AIMD
code) will have to wait until the accelerators get decent performance in
double precision.

2) The one exception is FFT and there is an implementation of FFT using
CUDA in CP2K.

3) CP2K can currently be compiled with FFT in single precision - I have
tested a build today (linked against a single precision build of FFTW)
and it seems to work.

I will have more to say on this topic, but let me split it into a
separate thread.

Best regards,
Ondrej


On Thu, Feb 5, 2009 at 22:21, Ben Levine <ben.l... at gmail.com> wrote:
>
> Hi Guys,
> Sorry to be joining the discussion a little late.  I haven't checked
> the group in a little while, I guess.
>
> Yes, I've done some work in incorperating some CUDA code into CP2K,
> and after a long hiatus I am just starting to work on it again.  Right
> now it is possible to run CP2K with a single precision FFT and several
> associated scatter/gather operations run on the GPU.  As others have
> said, running the FFT in single precision does not seem to degrade the
> accuracy of the calculation significantly.  In my experience this
> can't be said for other portions of the code, and this is the reason
> that greater CUDA support is not yet provided.
>
> To enable CUDA support compile with the -D__CUDA and -D__FFTSGL
> compiler flags...  But hold off for a little bit if you would.  I'm
> currently having some problems getting it to run in it's current
> state.  I'll post again when it's working.  Thanks for your interest.
>
> Ben
>
> On Jan 29, 8:59 am, Juerg Hutter <hut... at pci.uzh.ch> wrote:
>> Hi
>>
>>
>>
>> > I am interested in the status of GPGPU code in CP2K. So far, I have
>> > found only the very brief mention of single precision FFT using CUDA in
>> > the input manual and this e-mail from the CPMD archive:
>>
>> >http://www.cpmd.org/pipermail/cpmd-list/2008-April/004330.html
>>
>> > Could someone please give me a brief overview of the options one has in
>> > this area in CP2K? I would also like to know whether there is someone
>> > working on some sort of GPGPU code at this time.
>>
>> we have been looking into this a couple of times and also have some
>> accelerator cards available. Up to now we couldn't find a convincing
>> application, meaning a project together with a hardware setup where
>> the work/benefit ratio is good.
>>
>>
>>
>> > I also have one more specific question. Could FFTCU be adapted to use
>> > double precision capable cards? I am interested in this because of
>> > cluster calculations in open boundary conditions, where FFT seems to be
>> > the main bottleneck. Also, does anyone have any experience using FFTCU?
>>
>> we have some (but not comprehensive) experience with a setup where all
>> of CP2K is running double precicion except for the FFT. (compile with
>> -D__FFTSGL)
>> It seems that the loss in accuracy is not dramatic and this might be
>> an interesting option if a really fast single precision FFT is available.
>>
>> regards
>>
>> Juerg Hutter
>>
>> > Thanks a lot for any replies or comments,
>> > Ondrej
> >
>