Tips and FAQs

It takes too long time to compile a computational graph. Can I skip it?

Chainer does not compile computational graphs, so you cannot skip it, or, I mean, you have already skipped it :).

It seems you have actually seen on-the-fly compilations of CUDA kernels. CuPy compiles kernels on demand to make kernels optimized to the number of dimensions and element types of input arguments. Pre-compilation is not available, because we have to compile an exponential number of kernels to support all CuPy functionalities. This restriction is unavoidable because Python cannot call CUDA/C++ template functions in generic way. Note that every framework using CUDA require compilation at some point; the difference between other statically-compiled frameworks (such as cutorch) and Chainer is whether a kernel is compiled at installation or at the first use.

These compilations should run only at the first use of the kernels. The compiled binaries are cached to the $(HOME)/.cupy/kernel_cache directory by default. If you see that compilations run every time you run the same script, then the caching is failed. Please check that the directory is kept as is between multiple executions of the script. If your home directory is not suited to caching the kernels (e.g. in case that it uses NFS), change the kernel caching directory by setting the CUPY_CACHE_DIR environment variable to an appropriate path. See CuPy Overview for more details.

MNIST example does not converge in CPU mode on Mac OS X


Mac OS X is not officially supported. Please use it at your own risk.

Many users have reported that MNIST example does not work correctly when using vecLib as NumPy backend on Mac OS X. vecLib is the default BLAS library installed on Mac OS X.

We recommend using other BLAS libraries such as OpenBLAS.

To use an alternative BLAS library, it is necessary to reinstall NumPy. Here is an instruction to install NumPy with OpenBLAS using Homebrew.

$ brew tap homebrew/science
$ brew install openblas
$ brew install numpy --with-openblas

If you want to install NumPy with pip, use site.cfg file.

For details of this problem, see issue #704.

How do I accelerate my model using iDeep on Intel CPU?

Follow these steps to utilize iDeep in your model.

Install iDeep

The following environments are recommended by iDeep.

  • Ubuntu 14.04 / 16.04 LTS (64-bit) and CentOS 7 (64-bit)
  • Python 2.7.5+, 3.5.2+, and 3.6.0+

On recommended systems, you can install iDeep wheel (binary distribution) by:

$ pip install ideep4py

Enable iDeep Configuration

Currently iDeep is disabled by default because it is an experimental feature. You need to manually enable iDeep by changing chainer.config.use_ideep configuration to 'auto'. See Configuring Chainer for details.

The easiest way to change the configuration is to set environment variable as follows:

export CHAINER_USE_IDEEP="auto"

You can also use chainer.using_config() to change the configuration.

x = np.ones((3, 3), dtype='f')
with chainer.using_config('use_ideep', 'auto'):
    y = chainer.functions.relu(x)
<class 'ideep4py.mdarray'>

Convert Your Model to iDeep

You need to call model.to_intel64() (in the same way you call model.to_gpu() to transfer your link to GPU) to convert the link to iDeep.

Run Your Model

Now your model is accelerated by iDeep!

Please note that not all functions and optimizers support iDeep acceleration. Also note that iDeep will not be used depending on the shape and data type of the input data.

My training process gets stuck when using MultiprocessIterator

When you are using OpenCV somewhere in your code and the MultiprocessIterator is used in the training code, the training loop may get stuck at some point. In such situation, there are several workarounds to prevent the process got stuck.

  1. Set the environment variable as follows: OMP_NUM_THREADS=1
  2. Add cv2.setNumThreads(0) right after import cv2 in your training script.
  3. Use MultithreadIterator instead of MultiprocessIterator.

This problem is originally reported here: A training loop got stuck in a certain condition with multi-processing updater and opencv for Chainer and the discussion on related problems is still going here: OpenCV + Python multiprocessing breaks on OSX.