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From Tianqi Chen <>
Subject Re: [MXNET 2.0 Wishlist] [DISCUSS] Backend choices during runtime
Date Sun, 07 Apr 2019 21:45:26 GMT
While I personally like the idea. This can be something that is fairly
technical challenging and I would caution against this idea vs pushing for
good features and just allow runtime configuration.

The main problem here is due to the C++ ABI. There is no standard c++ ABI
across compilers, which means resorting to runtime DLL and dynamic loading
brings all sorts of technical problems, especially when multiple modules
depend on the same third dependency(CUDA runtime).
There is no good to go solution can be made here, especially given the
explosion of the backend variants and dependencies in C++.
A partial solution could be achieved, through the sole use of C ABI.
Combing this with code generation can result in some simplifications and
enable some runtime loadable module. TVM does this, and perhaps MXNet could
reuse some of that component for operator libraries. Similarly, having a
customizable operator library that is loadable via C ABI might be possible.

So to summarize, while I really like the idea of dynamically loadable
modules. My past experience suggests that this will bring a lot of
additional engineering burden and technical debts without significant
benefit. I would suggest starting by supporting something simple like a
plugin module, before moving toward the general direction.


On Sun, Apr 7, 2019 at 1:31 PM kellen sunderland <> wrote:

> Strongly support the idea of runtime loadable components in MXNet.  There's
> no reason (other than perhaps engineering effort) we can't have a single
> compilation of MXNet that finds dependencies and chooses execution paths
> intelligently (or based on configuration) at runtime.
> On Thu, Apr 4, 2019 at 12:29 PM Marco de Abreu <>
> wrote:
> > Hello,
> >
> > I'd like to start a discussion about something that I've noticed being
> > troublesome to maintain in the current version: Backend choices being
> made
> > at compile time.
> >
> > Right now, the different backends and accelerators (CPU, cuda, mkl, AWS
> > elastic inference, (future) AMD, openblas,TVM, etc) are all scattered
> > across the different layers of MXNet. On one hand, we have compile time
> > flags that decide which backends are being compiled into the binary,
> while
> > at the same time choices can be made in the frontend during runtime.
> >
> > At the moment, we have a lot of conditional build logic that picks
> > different parts. With the addition of MKLML and later MKLDNN the clear
> > separation of CPU and GPU got kind of broken up. While we have some
> places
> > where each code lives, in the end we resort to some files containing a
> lot
> > of conditional logic for the different backends (sorry I can't provide
> > links right now since I'm on mobile). To me this seems like a residue of
> > the fast development style from the early days (more processor statement
> > and less object orientation) while also having organic growth with new
> > accelerators. When I see how much AMD had to hack to fit in their
> > implementation, it seemed like we have to make this part more developer
> > friendly.
> >
> > At the moment, every new flavour of MXNet has to be entirely recompiled.
> > This makes it hard for users to figure out which options to use, while it
> > makes it harder for us to test since the overhead to test every single
> > combination of compile parameters would be overwhelming.
> >
> > I'd propose to have a clear class hierarchy based structure for
> > accelerators, operators and memory management. This structure can then be
> > implemented by the different backends. To reduce the compile burden, we
> > would introduce dynamic loading and split the different backends into
> > modules. These could then be developed, maintained and compiled on their
> > own and then placed in a "module" folder to be loaded at runtime. Adding
> a
> > new accelerator would be a matter of placing the precompiled binary into
> > the folder. The detailed configuration of that Backend would then be done
> > on runtime - the user shouldn't worry at the point of downloading mxnet
> > whether they want mkl, MKLDNN, mkl, openblas, atlas, TVM, cuda or what
> ever
> > else there is. I have an idea how we could help the user choosing, but
> > that's outside the scope of this proposal.
> >
> > This would allow us to have a "core" MXNet that takes care of the engine,
> > scheduling, communication and all the other crucial parts. On the other
> > hand we could make MXNet less of a monolith and have clear interfaces.
> This
> > would also act as a forcing function because the different parts wouldn't
> > be intermingled but have to follow the common interface.
> >
> > Of course this comes with the question what these interfaces would look
> > like. For operators, I'd like to propose getting inspiring (or fully
> > adapting) ONNX. For memory management and other Backend specific things
> we
> > could look at the current implementations and find a common ground.
> >
> > Back when I had a community driven project, we heavily used this
> modularity
> > and it brought great benefits - besides the fact that our core was closed
> > source. It allowed community developers to act entirely independent from
> > other parts and even allowed them to add their own logic without having
> to
> > touch the core. Thinking about companies that implement their own
> backends
> > or have special tweaked operators without wanting to disclose them, this
> > structure would avoid them having to fork the project and then spend a
> lot
> > of effort porting the changes to the latest source release versions.
> > Instead, they would maintain their module and we as MXNet community would
> > only have to maintain these interfaces.
> >
> > Right now this is a lot of prosa and basically a brain dump of my
> thoughts.
> > I'd be happy to follow up with details, but first I'd be curious what the
> > community thinks about this design.
> >
> > Best regards,
> > Marco
> >

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