Performance Best Practices

This guide explains some tips and advice for maximizing the performance of Chainer.

Use the Latest Version

It is generally recommended to use the latest version of Chainer and its dependent libraries (CUDA, cuDNN, iDeep, etc.). Some of the new features and performance optimizations introduced in newer versions of dependent libraries may not be available in older versions of Chainer. Also, Chainer itself is incrementally being improved to provide better performance.

If you are using Chainer v4 or later, you can check the version configuration by:

Chainer: 4.0.0
NumPy: 1.14.3
  CuPy Version          : 4.0.0
  CUDA Root             : /usr/local/cuda
  CUDA Build Version    : 9000
  CUDA Driver Version   : 9000
  CUDA Runtime Version  : 9000
  cuDNN Build Version   : 7100
  cuDNN Version         : 7100
  NCCL Build Version    : 2102

Generally, the Chainer team is maintaining the API between minor updates (e.g., v4.0 to v4.1) so that users can upgrade Chainer without modifying their code (see API Compatibility Policy for our policy). As for major updates, please refer to the Upgrade Guide to understand what should be done for migration.

Enable Hardware Accelerations

Using GPU

In most cases, running on GPU will give you better performance than on CPU. When using GPU, also make sure to install cuDNN, which is a library to accelerate deep neural network computations.


You don’t have to manually install cuDNN if you are using CuPy wheels, which includes the latest version of cuDNN. Check the output of chainer.print_runtime_info(); if you see the cuDNN version number, it is installed properly and will be used by Chainer automatically.


If you wish, you can manually disable use of cuDNN using chainer.config.use_cudnn configuration option. See Configuring Chainer for details.

Using CPU

If you are running Chainer on CPU, you can use iDeep to utilize vector instructions of CPU. See Tips and FAQs for steps to run your model with iDeep.

You can also improve performance by building NumPy linked to Intel MKL. See Numpy/Scipy with Intel® MKL and Intel® Compilers for the detailed instructions.


If you installed numpy package using Anaconda, you may already have MKL-linked NumPy. Check the output of numpy.show_config() to see what linear algebra library is linked.


Use of iDeep and MKL-linked NumPy are orthogonal. You can use both of them at once to maximize the performance.

Migrate Data Preprocessing Code from NumPy to CuPy

If you are preprocessing your dataset or running data augmentation using NumPy, you may be able to use CuPy as a substitution to improve performance.


It is not always efficient to use CuPy instead of NumPy, especially when the computation is not very heavy, or it cannot be done in batch.

Avoid Data Transfer

If you are using GPU, be aware of data transfer between CPU and GPU. For example, printing chainer.Variable on GPU (e.g., for debugging) will cause memory transfer from GPU to CPU, which will incur synchronization overhead.

You can use NVIDIA Visual Profiler to diagnose this kind of issue.

Optimize cuDNN Convolution

Workspace Size

Some convolution algorithms in cuDNN use additional GPU memory as a temporary buffer. This is called “workspace,” and users can adjust the upper limit of its size. By increasing the limit of workspace size, cuDNN may be able to use better (i.e., memory consuming but faster) algorithm.

The default size (in bytes) is:

>>> chainer.backends.cuda.get_max_workspace_size()

and can be adjusted using chainer.backends.cuda.set_max_workspace_size().

Maximum required workspace size may vary depending on various conditions such as GPU hardware and batch size of inputs.


Some convolution algorithms in cuDNN support the auto-tuner feature that finds the fastest convolution algorithm for given inputs. You can turn on this feature by setting autotune configuration to True.

See Configuring Chainer for detailed descriptions.


Auto-tuner tries to find the best algorithm for every first observation of the input shape combination. Therefore, the first batch will become slower when auto-tuner is enabled. The result of auto-tuner is cached on memory so that it can be reused for data with the same input shape combination. In other words, algorithm selected in the first batch will be reused for the second and later batches, as long as the input shape combination is the same.

If you set autotune configuration to False, the default convolution algorithm will always be selected, regardless of the previous auto-tuner results.


Auto-tuner always use the maximum workspace size.

Fine-Tune Configuration

There are some Chainer configuration values that affect performance. Although the default values work well in most cases, you can adjust the following configurations for better performance.

  • enable_backprop

    If you are running your model for inference (i.e., you don’t have to use back propagation because you are not training the model), you can set this configuration to False to improve performance and reduce memory consumption.

  • type_check

    By default, Chainer checks the integrity between input data and functions. This makes possible to display friendly message when, for example, data with invalid dtype or shape is given to a function. By setting this configuration to False, you can let Chainer skip such check to improve performance. It is recommended to turn off the check only for well-tested code and input data.

See Configuring Chainer for detailed descriptions.

Load Datasets Concurrently

If loading process of your dataset is I/O-bound or CPU-bound, consider using chainer.iterators.MultithreadIterator or chainer.iterators.MultiprocessIterator to load dataset concurrently using multiple threads or processes, instead of chainer.iterators.SerialIterator which works in a single thread in a single process.

Use Multiple GPUs

You can utilize multiple GPUs to make the training process faster.

For data parallelism, you can use or instead of For model parallelism, you need to manually transfer each chainer.Link in your model to each device.

See Using GPU(s) in Chainer for the working examples of each case.

Use Multiple Nodes

You can scale-out the training process of your Chainer model to multiple-node cluster by using ChainerMN, an additional package for Chainer which enables distributed deep learning. See ChainerMN Official Documentation for details.