[Openmp-dev] offloading to Nvidia GPUs

[Jeff Hammond via Openmp-dev]

According to LLNL RAJA team (https://github.com/LLNL/RAJA/issues/372#issuecomment-351795449), clang-ykt repo is stale and IBM progressing code in private repo for DOE/LLNL.

I have no idea when IBM will release latest GPU support but am optimistic that it will happen eventually. I can imagine that they’re focused on contract deliverables and don’t want to be distracted by other issues.

Jeff

Sent from my iPhone

> On Dec 18, 2017, at 7:33 AM, Jonas Hahnfeld via Openmp-dev <openmp-dev at lists.llvm.org> wrote:
> 
> Hi,
> 
> the answer is the same as in October: (upstream) Clang 5 doesn't fully support offloading to GPUs. Trunk's support has progressed since then but AFAIK still isn't able to link applications at the moment.
> 
> Regards,
> Jonas
> 
> Am 2017-12-18 16:11, schrieb Eichstaedt, Jan R via Openmp-dev:
>> Hello,
>> in addition to my previous mail:
>> I saw in this year's October archive, that Gabriele Jost has been
>> running into similar issue. Do you know if and how it has been
>> resolved for him?
>> Further, I tried out the clang-ykt git repo, and compiled in the same
>> fashion as I did with v5, which worked fine for some small test-cases.
>> This is why I am still quite surprised I ran into the mentioned
>> compile issue with v5. That said, I assume you merged the clang-ykt
>> branch into the v5 branch?
>> The problem with the clang-ykt branch for me however is, that I run
>> into some mysterious linking errors when compiling our major
>> framework.
>> Would you be able to kindly shed some light on this issue?
>> Thanks and kind regards,
>> Jan
>> -------------------------
>> FROM: Eichstaedt, Jan R
>> SENT: 14 December 2017 11:39:00
>> TO: Gheorghe-Teod Bercea
>> CC: via Openmp-dev
>> SUBJECT: Re: [Openmp-dev] offloading to Nvidia GPUs
>> Hello,
>> both your suggestions of adding the compile flags
>>    -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_35
>>    -Xopenmp-target -march=sm_35
>> still give me exactly the same error message.
>> Do you have any other suggestions?
>> Cheers,
>> Jan
>> -------------------------
>> FROM: Gheorghe-Teod Bercea <Gheorghe-Teod.Bercea at ibm.com>
>> SENT: 13 December 2017 18:30:00
>> TO: Eichstaedt, Jan R
>> CC: via Openmp-dev
>> SUBJECT: Re: [Openmp-dev] offloading to Nvidia GPUs
>> Hi,
>> Yes there is:
>> -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_35
>> You may also run into the problem that target offloading is not yet
>> fully supported.
>> Hope this helps!
>> Thanks,
>> --Doru
>> From:        "Eichstaedt, Jan R via Openmp-dev"
>> <openmp-dev at lists.llvm.org>
>> To:        via Openmp-dev <openmp-dev at lists.llvm.org>
>> Date:        12/13/2017 01:11 PM
>> Subject:        [Openmp-dev] offloading to Nvidia GPUs
>> Sent by:        "Openmp-dev" <openmp-dev-bounces at lists.llvm.org>
>> -------------------------
>> Hello,
>> I am using llvm and clang version 5.0.0 together with the openmp
>> project of that version on Ubuntu 16.04.
>> I try to compile a simple program involving a _#pragma omp target
>> teams distribute parallel for _statement to offload to a Nvidia-GPU
>> using the following flags:
>> -fopenmp=libomp -fopenmp-targets=nvptx64-nvidia-cuda
>> --cuda-path=/usr/local/cuda/ --cuda-gpu-arch=sm_35
>> However, the compilation fails, with the following being the first
>> assertion that is triggered:
>> clang++:
>> [...]/llvm-5.0.0.src/tools/clang/lib/Driver/ToolChains/Cuda.cpp:346:
>> virtual void
>> clang::driver::toolchains::CudaToolChain::addClangTargetOptions(const
>> llvm::opt::ArgList&, llvm::opt::ArgStringList&,
>> clang::driver::Action::OffloadKind) const: Assertion `!GpuArch.empty()
>> && "Must have an explicit GPU arch."' failed.
>> Is there a way to pass the GPU architecture differently? Or is target
>> offloading not fully supported in v5.0.0 yet and I might better use
>> the clang-ykt project? Or have I overlooked something else completely?
>> Thanks for any help you can offer.
>> Cheers,
>> Jan
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