[llvm-dev] [cfe-dev] [Openmp-dev] RFC: Proposing an LLVM subproject for parallelism runtime and support libraries

Andrey Bokhanko via llvm-dev
Mon, 09 May 2016 18:03:51 -0000

Thanks Jason (and Chandler) to tell Chandler's opinion, though it still
doesn't answer my original question:

> Both SE and libomptarget are libraries that handle offloading, not
parallelism. I understand other libraries, to be added in the future, might
deal with parallelism, but maybe we need a separate project for them?
(Something Chris already hinted.)

The example simply adds confusion

> One example he brought up was AVX 512. He thinks that code explicitly
targeting CPU parallelism should also be included in this project, even
though it doesn't fit in the category of "offloading".

Do we want to add a vectorizer to this project as well?

Yours,
Andrey

On Mon, May 9, 2016 at 8:32 PM, Jason Henline <jhen at google.com> wrote:

> I talked to Chandler about the name "offload_libs" vs
"parallel_libs" and
> he said he thinks "offload" is too narrow of a term for the scope
he sees
> for this subproject. One example he brought up was AVX 512. He thinks that
> code explicitly targeting CPU parallelism should also be included in this
> project, even though it doesn't fit in the category of
"offloading". So
> that is an argument in favor of "parallel_libs" instead of
"offload_libs".
>
> Chandler, please correct me if I misrepresented your thoughts on this.
>
> On Thu, Apr 28, 2016 at 9:55 AM Jason Henline <jhen at google.com>
wrote:
>
>> Alexandre,
>>
>> Thanks for your thoughts on this. I was thinking that each subproject
>> library would be responsible for handling its own name and any
associated
>> branding. For example, when evangelizing for StreamExecutor, I plan to
>> refer to it as StreamExecutor, not parallel_libs-StreamExecutor or
>> something like that. So I think it is OK for the top-level container
>> project to have an undistinguished name. Does that sound reasonable?
>>
>> On Thu, Apr 28, 2016 at 7:09 AM Alexandre Eichenberger <alexe at
us.ibm.com>
>> wrote:
>>
>>> A suggestion on naming: by choosing too generic a name, you
don't get
>>> any branding.
>>>
>>> My point for the omp library: if someone talks about GOMP, KMPC /
IOMP,
>>> or LOMP, they would know we are talking about the GNU, Intel, IBM
>>> implementation. I don't think we get that with OMP, which was
selected for
>>> the OMP runtime.
>>>
>>> So I would suggest to append "llvm" or "lr" for
LLVM runtime, or
>>> something distinctive that you like.
>>>
>>> This make sense because users will have choices of runtimes, gcc
linking
>>> to GOMP, LLVM runtime, LOMP on POWER; GOMP, LLVM, IOMP on Intel...
and we
>>> will need to educate our users on which one to use.
>>>
>>> Alexandre
>>>
>>>
>>>
-----------------------------------------------------------------------------------------------------
>>> Alexandre Eichenberger, Master Inventor, Advanced Compiler
Technologies
>>> - research: compiler optimization (OpenMP, multithreading, SIMD)
>>> - info: alexe at us.ibm.com
http://www.research.ibm.com/people/a/alexe
>>> - phone: 914-945-1812 (work) 914-312-3618 (cell)
>>>
>>>
>>>
>>> ----- Original message -----
>>> From: Andrey Bokhanko via cfe-dev <cfe-dev at lists.llvm.org>
>>> Sent by: "cfe-dev" <cfe-dev-bounces at
lists.llvm.org>
>>> To: Jason Henline <jhen at google.com>
>>>
>>> Cc: llvm-dev <llvm-dev at lists.llvm.org>, clang developer
list <
>>> cfe-dev at lists.llvm.org>, "openmp-dev at
lists.llvm.org" <
>>> openmp-dev at lists.llvm.org>
>>> Subject: Re: [cfe-dev] [Openmp-dev] [llvm-dev] RFC: Proposing an
LLVM
>>> subproject for parallelism runtime and support libraries
>>> Date: Thu, Apr 28, 2016 9:23 AM
>>>
>>> Jason,
>>>
>>> Very nice write-up. Well done!
>>>
>>> My two kopecks (before you asked, one kopeck is the smallest item
of
>>> currency in Russia ;-)):
>>> * Bugzilla and mailing list requirements are not covered. Do you
want to
>>> have a component in Bugzilla for each project? One for all of them?
Mailing
>>> list -- a separate list for each project? (IMHO, an overkill) One
for all
>>> of them?
>>> * Build system -- I suppose you expect all of the libs to be built
>>> separately, without a single unified cmake file. Correct? Also, I
expect
>>> you want all of the libs to be integrated into LLVM build --
correct? This
>>> should be spelled out explicitly.
>>> * I don't really like "parallel" in the name. Both SE
and libomptarget
>>> are libraries that handle offloading, not parallelism. I understand
other
>>> libraries, to be added in the future, might deal with parallelism,
but
>>> maybe we need a separate project for them? (Something Chris already
>>> hinted.) How about "offloading_lib"?
>>>
>>> Yours,
>>> Andrey
>>>
>>>
>>> On Wed, Apr 27, 2016 at 7:58 PM, Jason Henline via Openmp-dev <
>>> openmp-dev at lists.llvm.org> wrote:
>>>
>>> I've put together a proposed "charter" for this new
project, which I am
>>> calling parallel_utils (although I'm very open to suggestions
for a better
>>> name). The text of my charter is below, and I welcome any input on
how it
>>> can be improved.
>>>
>>>
>>> ====================================================>>>
LLVM Parallel Utils Subproject Charter
>>> ====================================================>>>
>>> ----------------------------------------------
>>> Description
>>> ----------------------------------------------
>>> The LLVM open source project will contain a subproject named
>>> `parallel_utils` which will host the development of libraries which
are
>>> aimed at enabling parallelism in code and which are also closely
tied to
>>> compiler technology.  Examples of libraries suitable for hosting
within the
>>> `parallel_utils` subproject are runtime libraries and parallel math
>>> libraries. The initial candidates for inclusion in this subproject
are
>>> StreamExecutor and libomptarget which would live in the
`streamexecutor`
>>> and `libomptarget` subdirectories of `parallel_utils`,
respectively.
>>>
>>> The `parallel_utils` project will host a collection of libraries
where
>>> each library may be dependent on other libraries from the project
or may be
>>> completely independent of any other libraries in the project. The
rationale
>>> for hosting independent libraries within the same subproject is
that all
>>> libraries in the project are providing related functionality that
lives at
>>> the intersection of parallelism and compiler technology. It is
expected
>>> that some libraries which initially began as independent will
develop
>>> dependencies over time either between existing libraries or by
extracting
>>> common code that can be used by each. One of the purposes of this
>>> subproject is to provide a working space where such refactoring and
code
>>> sharing can take place.
>>>
>>> Libraries in the `parallel_utils` subproject may also depend on the
LLVM
>>> core libraries. This will be useful for avoiding duplication of
code within
>>> the LLVM project for common utilities such as those found in the
LLVM
>>> support library.
>>>
>>>
>>> ----------------------------------------------
>>> Requirements
>>> ----------------------------------------------
>>> Libraries included in the `parallel_utils` subproject must strive
to
>>> achieve the following requirements:
>>>
>>> 1. Adhere to the LLVM coding standards.
>>> 2. Use the LLVM build and test infrastructure.
>>> 3. Be released under LLVM's license.
>>>
>>>
>>> Coding standards
>>> ----------------
>>> Libraries in `parallel_utils` will match the LLVM coding standards.
For
>>> existing projects being checked into the subproject as-is, an
exception
>>> will be made during the initial check-in, with the understanding
that the
>>> code will be promptly updated to follow the standards. Therefore, a
three
>>> month grace period will be allowed for new libraries to meet the
LLVM
>>> coding standards.
>>>
>>> Additional exceptions to strict adherence to the LLVM coding
standards
>>> may be allowed in certain other cases, but the reasons for such
exceptions
>>> must be discussed and documented on a case-by-case basis.
>>>
>>>
>>> LLVM build and test infrastructure
>>> ----------------------------------
>>> Using the LLVM build and test infrastructure currently means using
>>> `cmake` for building, `lit` for testing, and `buildbot` for
automating
>>> build and testing. This project will follow the main LLVM project
>>> conventions here and track them as they evolve.
>>>
>>>
>>> LLVM license
>>> ------------
>>> For simplicity, the `parallel_utils` project will use the normal
LLVM
>>> license. While some runtime libraries use a dual license scheme in
LLVM, we
>>> anticipate the project removing the need for this eventually and in
the
>>> interim follow the simpler but still permissive license. Among
other
>>> things, this makes it straightforward for these libraries to re-use
core
>>> LLVM libraries where appropriate.
>>>
>>> On Wed, Apr 27, 2016 at 9:52 AM Jason Henline <jhen at
google.com> wrote:
>>>
>>> Andrey,
>>>
>>> I may have misunderstood Chandler, but I think it would be good to
house
>>> libomptarget together with SE in the new project. I suspect he
means to
>>> leave the option open for the libomptarget developers to choose the
best
>>> option as they see fit.
>>>
>>> In terms of organization, I would expect the project initially to
>>> contain a StreamExecutor directory and a libomptarget directory
where each
>>> project could work separately.
>>>
>>> When it comes to the difference in review process between the two
>>> projects, I don't know the answer. I would expect the new
project to handle
>>> reviews similar to the way they are handled in the LLVM project
itself, so
>>> I don't know if there would be any difference compared to what
is happening
>>> now with libomptarget.
>>>
>>> On Wed, Apr 27, 2016 at 9:32 AM C Bergström <openmp-dev at
lists.llvm.org>
>>> wrote:
>>>
>>> I respect Hal's more tactful approach and response..
>>>
>>> Let me play devils advocate for a minute
>>>
>>> 1) Yet another programming model - Is the advantage spelled out
>>> somewhere? (I know there are reasons, but I'd like to see a FAQ
or
>>> this clearly documented. Examples pretty please.. More for long
term
>>> than my own selfish benefit)
>>> 2) Is this an "open standard" - If I wanted to propose a
major change
>>> to SE - how would I or someone else go about it? OpenMP/ACC have
more
>>> or less clearly defined paths for new features.. What's the
governing
>>> policy here.. Bug fixes are easy to deal with, but does Google have
>>> final say on the roadmap..
>>> 3) When the project is created - will it include lots of good
tests?
>>> 4) It's probably used internally @google - who else will be
using
>>> this? Is the target HPC, Android.. etc
>>>
>>> Lastly - sorry, but I don't like this kick-the-can approach to
what
>>> should be proper engineering and planning upfront. Can someone
@google
>>> gentleman's promise to actively work on playing nice with other
>>> projects, specifically OpenMP and Intel. From my perspective
nothing
>>> stops Google from tossing it up on github or google code and
letting
>>> it stay there until all the pieces are in the correct place. Why it
>>> *must* be an llvm project now doesn't make sense to me. When
the shoe
>>> was on the other foot (OpenMP) there was all sorts of shit and
redtape
>>> Intel (and others) had to jump around to get it included. Google
has a
>>> lot of good karma in the llvm community and maybe that's the
>>> difference..
>>> _______________________________________________
>>> Openmp-dev mailing list
>>> Openmp-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>>>
>>>
>>> _______________________________________________
>>> Openmp-dev mailing list
>>> Openmp-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
>>>
>>>
>>> _______________________________________________
>>>
>>>
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>>>
>>>
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