[Openmp-dev] Available features of libomptarget nvptx for 7.0 release

Guray Ozen via Openmp-dev openmp-dev at lists.llvm.org
Thu Jul 5 05:06:07 PDT 2018

Georgios and Alexey, Thank you very much answers.

1. It is good to know that teams reduction is not ready yet. Then I will stay tuned. Just one quick question, does new design affect parallel reduction?
2. I am following the submission about bundler. It is affecting us directly since we use clang's driver along with OpenMP toolchain.

In terms of data sharing -  I am aware of data sharing issue. It is an inevitable problem :) We are not there yet at the moment.

From: Alexey Bataev <a.bataev at outlook.com>
Sent: Tuesday, July 3, 2018 7:04 PM
To: Guray Ozen <gozen at nvidia.com>; Hervé Yviquel <herve.yviquel at ic.unicamp.br>; openmp-dev at lists.llvm.org
Subject: Re: [Openmp-dev] Available features of libomptarget nvptx for 7.0 release

Hi Guray,

Almost all my comments, related to clang, also related to libomptarget.

1. Reductions across the teams. We don't have support for this neither in clang, nor in runtime. I don't like the implementation in clang-ykt and declined to include this implementation in trunk. Instead I proposed the new design of the reductions across the teams mechanism (it is more universal, stable and extendable). One of our engineers works on this feature for libomptarget, but it is hard to say when it is going to be ready.

2. Yes. Again, we had a long discussion. I'm highly against the solution, which is part of the clang-ykt, and proposed a new design. Again, one of our engineers is working on this feature along with the generic data-sharing problem. Probably, you will face the same data-sharing problem, we ran into, and you will also need the support these 2 data-sharing models: cuda-like and the generic, which is a kind of the original C++ model, where locals can be accessed by all the threads in the parallel region.


Best regards,

Alexey Bataev
03.07.2018 12:48, Guray Ozen пишет:
Thank you very much for the answer Alexey. I am actually more curious about the runtime. Because, in Nvidia, we have started implementing OpenMP GPU offload on Flang frontend. We are using libomptarget and libomtparget-nvptx. Therefore I was asking which features will runtime support in v7.0.
Also, my additional comments are below.
From: Alexey Bataev <a.bataev at outlook.com><mailto:a.bataev at outlook.com>
Sent: Tuesday, July 3, 2018 5:39 PM
To: Hervé Yviquel <herve.yviquel at ic.unicamp.br><mailto:herve.yviquel at ic.unicamp.br>; Guray Ozen <gozen at nvidia.com><mailto:gozen at nvidia.com>; openmp-dev at lists.llvm.org<mailto:openmp-dev at lists.llvm.org>
Subject: Re: [Openmp-dev] Available features of libomptarget nvptx for 7.0 release

Hi, are you interested in the status of clang compiler or just library? I can answer for clang and support for offloading to NVidia GPUs.
It supports almost everything from OpenMP 4.5, except for reductions across the teams.

[GURAY:] Is it only in clang ? Do you know does teams reduction works on runtime?

Also, there are still some bugs in the current implementation.
1. Some math functions may cause troubles during the compilation of the device specific code. There is a patch that fixes that problem, but it requires some additional work.
2. Our implementation supports 2 datasharing model for the device code: cuda mode, where all local variables are actually local threadprivate globals (i.e. registers), and generic mode, where the shared variables are placed in the global memory and can be shared between the threads of the parallel regions. Currently, only cuda-mode works correctly, generic mode requires some additional bug fix.
Also, trunk clang compiler does not support static linking.

[GURAY:] Is related to clang-offload-bundler?

Best regards,
Alexey Bataev.


Best regards,

Alexey Bataev
01.07.2018 5:26, Hervé Yviquel via Openmp-dev пишет:
I agree. Would it be possible to get an update on the status of libomptarget and its codegen? Is it more or less in pair with clang-ykt now?


On juin 13 2018, at 6:15 pm, Guray Ozen via Openmp-dev <openmp-dev at lists.llvm.org><mailto:openmp-dev at lists.llvm.org> wrote:

Hi all,

The release date for 7.0 is approaching. I'm curious about the libomptarget and libomptarget-nvptx runtime library. Is there a list of which features are not available in 7.0 and which ones are not?



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