[llvm-dev] Should we have a "GPU working group"?

Thu Nov 11 11:42:17 PST 2021

+1. Happy to help with organizing, notes, etc.

On Thu, Nov 11, 2021 at 1:58 PM Min-Yih Hsu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> On Nov 11, 2021, at 10:22 AM, Jason Eckhardt via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> +1 here as well, even if in lurk mode initially.
>
> Some additional topics of interest:
>
>    1. *Occupancy vs resource trade-offs (especially registers)*. Requires
>    closer coordination of scheduling + register allocation, in addition to
>    extensions in each.
>    2. *Divergence analysis/uniformity analysis*. Applications to sync
>    insertion, scalar vs vector register allocation, instruction selection, etc.
>    3. *Synchronization insertion*. Some GPUs have instructions to hint
>    where a good re-convergence point is.
>    4. *Global instruction scheduling*. Some GPU code is surprisingly
>    branchy. Numerous out-of-tree/proprietary global schedulers have been
>    written, we *still* don't have one upstream.
>
> I’m interested on this. Can you list some (public available) works?
>
>
>    1. I*ncreasing overall back-end speed for JIT compilation*. GPU
>    back-ends are often situated within graphics drivers where they dynamically
>    compile shaders with absurdly stringent timing constraints. GlobalISel is a
>    step in the right direction, but more needs doing (particularly for small
>    shaders).
>
> This brings benefits to a wider community so I’m definitely +1 on it.
> Also, I believe there are some ongoing efforts on porting codegen pipeline
> to use the new PassManager. Which has the potential to speed up the
> compilation speed.
>
> As an example, #1 is handled (if at all) specially by each target. With
> the proliferation of GPUs (Teams Red, Green, Blue, and others), it would be
> useful for "all boats to float higher" with generic code (with
> target-specific hooks/overrides) supported by the wider community as
> opposed to redundant re-invention of the wheel (or no wheel at all, as in
> #4). Then specific targets can expend effort adding value for their
> particular needs.
>
> ------------------------------
> *From:* llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Lei Zhang
> via llvm-dev <llvm-dev at lists.llvm.org>
> *Sent:* Thursday, November 11, 2021 9:44 AM
> *To:* Valentin Churavy <v.churavy at gmail.com>
> *Cc:* Lieberman, Ron <Ron.Lieberman at amd.com>; justin.lebar at gmail.com <
> justin.lebar at gmail.com>; Chesterfield, Jonathan <
> Jonathan.Chesterfield at amd.com>; llvm-dev at lists.llvm.org <
> llvm-dev at lists.llvm.org>; tianshilei1992 at gmail.com <
> tianshilei1992 at gmail.com>; Rodgers, Gregory <Gregory.Rodgers at amd.com>;
> Huber, Joseph <huberjn at ornl.gov>; Narayanaswamy, Ravi <
> ravi.narayanaswamy at intel.com>
> *Subject:* Re: [llvm-dev] Should we have a "GPU working group"?
>
> *External email: Use caution opening links or attachments*
> +1. There are certainly efforts that need broad collaboration among
> various interest parties; they would benefit from more interactive
> discussions to have everybody on the same page. What immediately jumps into
> my mind include how we can push to have unified/better SPIR-V support in
> LLVM proper / cross LLVM/MLIR, etc. It's a big one that I'd assume will
> take a long time to unfold and will have back and forth. Having a place to
> discuss will actually make sure we put efforts towards it (or at least have
> plans and revisit periodically). There are certainly many other topics to
> discuss too, as said by Johannes. I think this is a great idea.
>
> Thanks,
> Lei
>
>
> On Wed, Nov 10, 2021 at 4:03 PM Valentin Churavy via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> I would certainly be interested in joining such an effort.
>
> -V
>
> On Wed, Nov 10, 2021 at 3:56 PM Johannes Doerfert via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Hey,
>
> We nowadays have various "working groups" that meet regularly to discuss
> technical topics (incl. RISC-V, MLIR, OpenMP, Alias Analysis, ML, Flang,
> ...).
> It's a reasonably nice way for people to connect and present ideas, get
> feedback, etc. in an interactive environment.
> While the OpenMP meeting has a strong emphasis on offloading, we do not
> meet to discuss "generic GPU" topics as a community.
>
> This email is to determine if people would be interested in meeting once
> every N weeks (initially we could say 2) to coordinate efforts in this
> space, e.g., development of GPU-specific optimizations, organization of
> driver and backend code, dealing with issues like convergent functions, ...
>
> I CC'ed a bunch of people that might want to join such a meeting but
> certainly this is something everyone would be invited to and I hope
> people forward this to parties that might not read llvm-dev.
>
> Looking forward to hear what people think :)
>
> ~ Johannes
>
>
>
>
> --
> ───────────────────
> ∽ Johannes (he/his)
>
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