+1 towards having a single build system

I'd like to add the benefit of this approach allowing us to have the same
build logic across all operating systems. It would be great if we could
make x86/Unix, x86/windows, x86/mac and ARM/Unix first class citizens from
the beginning.

-Marco

Kellen Sunderland <kel...@apache.org> schrieb am Do., 4. Apr. 2019, 12:31:

> Hello MXNet devs,
>
> I'd like to start a thread discussing what our build system should look
> like in MXNet 2.0.  I'd propose that although the current make system has
> served us well in the past, we remove it along with the bump to 2.0.  The
> end goal I'd like to see is that we have a clean build system, without a
> bunch of conditional logic that makes contributing and testing MXNet a
> simpler process.  Additionally I'd propose we target a minimum cmake
> version of 3.7 for reasons described below.
>
> First I'd like to give some context on why I'd propose we don't just switch
> to cmake, but we also target a relatively new version (version 3.7 from
> Nov, 2016) of cmake.  The largest benefits in making this change would
> apply to CUDA builds where cmake itself has quite inconsistent
> functionality between versions.  One persistent annoyance I've had with
> cmake is that we've had conditional logic for the FindCUDA command which at
> one point targeted some modern cmake features, but then in subsequent
> versions of cmake the way these features works was tweaked, and now I find
> these cmake features are consistently broken to the point that I require a
> bunch of -D defines to compile properly or to use an IDE.  An additional
> CUDA related issue is that every time there's a new SM added to NVCC we
> have to make a few source changes to support it.  I could see this being
> problematic for users who may suddenly realize that due to their
> compilation settings, they may not actually be enabling the features they
> think they are with their shiny new GPUs.
>
> As an alternative if we, for example, target cmake 3.7 at a minimum, and we
> want to find cuda and then build a list of reasonable PTX/BINS we could use
> the following command[1]:
>
> ----
> FindCUDA(...)
> ...
> CUDA_SELECT_NVCC_ARCH_FLAGS(ARCH_FLAGS 3.0 3.5+PTX 5.2(5.0) Maxwell)
>   LIST(APPEND CUDA_NVCC_FLAGS ${ARCH_FLAGS})
> ----
>
> Simple, concise, and it would help to make the building experience more
> consistent across platforms, build environments and IDEs (looking at you
> CLion).  We'd of course need to do a little experimentation work to make
> sure that this does indeed work as intended, and can replace the currently
> complex findCuda logic we have in our build systems, but for the sake of
> the proposal let's assume these cmake commands do indeed work consistently
> as documented from cmake 3.7 onwards.
>
> To give users a chance to update their tooling I'd also suggest we begin
> warning users at least a release in advance that make based builds will be
> deprecated in MXNet 2.0 so they can begin migrating to cmake.  I'd also
> want to display deprecation messages for unused cmake flags (such as the
> profiler flag) for a release before the 2.0 release, and then remove them
> in 2.0.
>
> Of course not all users have cmake 3.7 on their systems, some of our
> employers force use to use ridiculously outdated linux distributions.  The
> good news for these users is that if we can offer Docker compilation with
> an image that has a supported version of cmake and we should be able to
> build a portable binary that work even with very old distributions of
> Linux.  Additionally installing cmake from source is also fairly
> straightforward [2] and works quite well on older distros in my experience.
>
> Looking forward to hearing what others think.  Any preferred build systems
> that you all would want to use?  Is cmake the right system to centralize
> on?  If so, is version 3.7 a reasonable minimum version to target?  Is the
> 2.0 release a good point at which we can think about simplifying build
> logic?
>
> 1: https://cmake.org/cmake/help/v3.7/module/FindCUDA.html
> 2: https://github.com/Kitware/CMake
>

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