[gmx-developers] OpenACC Development

[Millad Ghane]

Hi Berk,

Thanks for your reply.

I know that OpenACC is a programming language. What I meant by OpenACC
architecture was "OpenACC software architecture". I know that eventually,
the OpenACC code is executed by an underlying hardware architecture (which
could be NVidia or AMD/ATI or even Xeon PHI from Intel).

What I hope to achieve: introducing a set of kernels that are optimized
for OpenACC.
What I have done: trying to parallelize the 4x4 Plain-C code for CPU using
OpenACC compiler directives.

The problem is that the code and especially the data structures (in
Plain-C CPU kernels) get complex in kernel level to some extent.
Therefore, that was what I was looking for: introducing kernels for
OpenACC programming model.


Best Regards,
Millad




> Hi Millad,
>
> Welcome to the list.
>
> GROMACS aims for close to optimal performance on all relevant hardware.
> To achieve this, we write highly optimized non-bonded (and other)
> kernels for all relevant architectures. Currently we have plain-C CPU
> kernels (extremely slow), SIMD, CUDA and OpenCL non-bonded kernels. The
> optimization is not so much in the arithmetics, but rather in the data
> layout. OpenACC is not an architecture, but a programming standard. So
> you would need to choose a target architecture for your OpenACC
> "acceleration" and then choose one of our kernel types. But the only
> gain of this would be semi-automated offloading. The question is then if
> the offloading will be efficient enough.
>
> Cheers,
>
> Berk
>
> On 2016-07-01 02:05, Millad Ghane wrote:
>> Hello everyone,
>>
>> I am a PhD student in computer science at University of Houston.
>> Currently, in this Summer as an intern, I am working with the physics
>> department in our school to work on GROMACS in order to port it to
>> OpenACC. My adviser for this project is Prof. Cheung.
>>
>> My understanding is that GROMCS currently supports NVIDIA GPUs (and also
>> SIMDs on CPUs), however my job is to investigate the ability of
>> transferring the code to OpenACC, which is more heterogeneous and
>> ubiquitous compared to CUDA.
>>
>> My question regarding the development of GROMACS is that whether you are
>> supporting or planning to support OpenACC currently or in future. And,
>> if
>> you are not supporting OpenACC, my question is that how can I introduce
>> new "kernel functions" for supporting OpenACC. How much work should be
>> done?
>>
>> Based on my understanding, you had different kernel function for
>> different
>> architectures (CPU, CPU with SIMD, GPU). I wanted to know how much
>> effort
>> is required to introduce new architecture like OpenACC?
>>
>> Before getting in touch with you, I dig into some of the code and tried
>> to
>> parallelize the CPU version of kernel code using OpenACC constructs, but
>> the code gets messy and the data is not transferred correctly on the
>> device. So, my hope is to introduce new kernels for OpenACC like the way
>> you introduced different ones for CPUs and GPUs. This way, we have more
>> controls over data transfers and kernel codes.
>>
>>
>> I hope I was clear enough and make you interested.
>>
>>
>> Best Regards,
>> Millad Ghane
>> Computer Science Department
>> University of Houston
>>
>>
>
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