We have a systematic solution to go without ABI headache. I am struggling with some errants, and will share our proposal here as soon as I could. This will be very interesting topic to discuss. Let's work hard together and make it perfect :-)
On Thu, Apr 11, 2019 at 12:43 PM Pedro Larroy <pedro.larroy.li...@gmail.com> wrote: > Thanks Marco for raising this issue. I think we can certainly do some > improvements in modularization and build. At the same time Tianqi's > point of view is important to consider and on point. I see a high risk > of overengineering in such endeavor. > > I also see increased complexity, difficulty debugging, C++ ABI > headaches, API compatibility, crashes inside a binary module, etc. > which I don't want to deal with as a developer or even as an MXNet > user. Does somebody have answers to these problems? > > If somebody thinks they have a good solution, by all means propose a > design in the wiki, I think we are all open. Personally I see several > other lower hanging fruits which need our attention: > * Simplifying our build logic, > * Cuda selection in CMake, > * Reducing the abuse of inlined code moving more logic to > implementation files and improve scoping which will also speed up > compilation, (some units take more than 5 minutes to build and lots of > RAM in a top of the line CPU core) > * Reduce runtime of some unit tests > And other improvements in our codebase that would bring immediate > benefits without the risks of overengineering of a plugin system. I > also question our bandwidth for such an endeavor. > * Improve MXNet startup time. > * Thread safety > > I would say, let's apply the KISS principle, let's make the project > fast to build, easy to work on, well documented and easy to contribute > to before building the next Netscape browser. Otherwise we could save > ourselves this exercise and switch to Rust directly. > > Pedro. > > > > On Mon, Apr 8, 2019 at 9:42 AM Tianqi Chen <tqc...@cs.washington.edu> > wrote: > > > > Just to clarify. I am not questioning the usefulness of the separation. > > Just want to highlight the technical challenges here based on our past > > experiences. > > > > Crossing DLL boundaries in C++ can create quite a lot of problems, > > especially some of the dependencies used a different version of the > > compiler, follows static packaging or simply because of the dynamic > linking > > difference in windows. These problems could make this direction move less > > appealing compared to focusing effort on other things. > > > > Technically, as a first step, it is possible to make dependencies change > > not change the global header files and via registration so that changing > > certain component won't trigger a global recompile in CMake. This is > also a > > required step toward some modularity. > > > > For plugins, solutions that use C ABI can be used for certain plugin > > modules. > > > > Some of the discussion has been tied to what the interface should look > > like. I think we should use different threads for these and puts in more > > thoughts. > > > > Tianqi > > > > > > > > On Sun, Apr 7, 2019 at 4:39 PM kellen sunderland < > > kellen.sunderl...@gmail.com> wrote: > > > > > I think we can make some incremental progress. My thoughts were along > the > > > lines of plugins (thinking about what happens with the VLC project). > At > > > process launch time we could gather some information about our > execution > > > environment (either through configuration, or by convention looking at > our > > > folder structure and libraries available). We could then later load > the > > > components we need after understanding if we're using a CUDA backend > and > > > what operators or subgraph components we would need. Advantages would > be > > > that we would move a lot of the current conditional compile logic to > > > runtime, and automate a lot of it. It would also make packaging > binaries > > > for targeted environments a little easier. As an example we could > compile > > > once, then remove CUDA focused libraries for systems that are going to > run > > > on CPUs. > > > > > > On Sun, Apr 7, 2019 at 2:45 PM Tianqi Chen <tqc...@cs.washington.edu> > > > wrote: > > > > > > > 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. > > > > > > > > Tianqi > > > > > > > > On Sun, Apr 7, 2019 at 1:31 PM kellen sunderland < > > > > kellen.sunderl...@gmail.com> 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 < > marcoab...@apache.org> > > > > > 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 > > > > > > > > > > > > > > > > > > >
