[Openmp-dev] [RFC] Device runtime library (re)design

[Jon Chesterfield via Openmp-dev]

>
> Thanks for the RFC. I think I've caught up on the thread and associated
patches. I'm late to the party so this email is a bit long.

Today we have a working nvptx implementation in tree. There's also a
working implementation for amdgcn on githib. @Ravi if yours is open source
I'd love to compare the implementations, if not, I'd invite you to look at
https://github.com/ROCm-Developer-Tools/llvm-project/tree/AOMP-190715/openmp/libomptarget/deviceRTLs

Largely shared code would make bringing up new devices easier if the
abstractions are in the right place and otherwise more difficult. I'm wary
of significantly rewriting the code while only a single target is supported
in case we draw the lines in the wrong place. To that end, we (amd) would
like to add our target. That'll remove some hard coded nvptx behaviour and
hopefully reduce the cost of adding a third accelerator.

Right now, there's zero code shared with nvptx. We copied the cuda and
#ifdef'ed the parts that differ. That's too expensive to maintain under
churn to 'common' code and not something I'd like to commit as is. Instead,
I'd like to incrementally refactor the deviceRTL to extract nvptx specific
stuff, with close reference to our GitHub repo, until the difference is so
slight that we can upstream a couple of files and some cmake to bring
amdgcn online.

Reducing the use of cuda, bringing the code more inline with LLVM's coding
style, documenting target bring up are all great goals. I think that can
also be done incrementally and is largely orthogonal to getting some target
diversity in the codebase. I'd like to be involved in both tracks.

As a concrete, minimal proposal, I'd like to put the functions that use
nvptx asm behind a zero runtime overhead interface and get that up for
review.

Thanks all,

Jon




---------
>

> Message: 1
> Date: Thu, 11 Jul 2019 19:09:19 +0000
> From: "Doerfert, Johannes via Openmp-dev" <openmp-dev at lists.llvm.org>
> To: "Narayanaswamy, Ravi" <ravi.narayanaswamy at intel.com>, "Bae,
>         Hansang" <hansang.bae at intel.com>, "Tian, Xinmin"
>         <xinmin.tian at intel.com>
> Cc: "openmp-dev at lists.llvm.org" <openmp-dev at lists.llvm.org>
> Subject: Re: [Openmp-dev] [RFC] Device runtime library (re)design
> Message-ID:
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> DM6PR09MB39622938E09D6E11080F6838BAF30 at DM6PR09MB3962.namprd09.prod.outlook.com
> >
>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Yes, the RFC I send to openmp-dev has three example patches that clean up
> the code, add documentation, and extract target specific 16
> ******************************************
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