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Table of Contents

  1. Contributing to CUB
  2. CMake Options
  3. Development Model

Contributing to CUB

CUB uses Github to manage all open-source development, including bug tracking, pull requests, and design discussions. This document details how to get started as a CUB contributor.

An overview of this process is:

  1. Clone the CUB repository
  2. Setup a fork of CUB
  3. Setup your environment
  4. Create a development branch
  5. Local development loop
  6. Push development branch to your fork
  7. Create pull request
  8. Address feedback and update pull request
  9. When your PR is approved...

Clone the CUB Repository

To get started, clone the main repository to your local computer:

git clone https://github.com/thrust/cub.git
cd cub

Setup a Fork of CUB

You'll need a fork of CUB on Github to create a pull request. To setup your fork:

  1. Create a Github account (if needed)
  2. Go to the CUB Github page
  3. Click "Fork" and follow any prompts that appear.

Once your fork is created, setup a new remote repo in your local CUB clone:

git remote add github-fork [email protected]:<GITHUB_USERNAME>/cub.git

Setup Your Environment

Git Environment

If you haven't already, this is a good time to tell git who you are. This information is used to fill out authorship information on your git commits.

git config --global user.name "John Doe"
git config --global user.email [email protected]

Configure CMake builds

CUB uses CMake for its developer build system. To configure, build, and test your checkout of CUB with default settings:

# Create build directory:
mkdir build
cd build

# Configure -- use one of the following:
cmake ..   # Command line interface.
ccmake ..  # ncurses GUI (Linux only)
cmake-gui  # Graphical UI, set source/build directories in the app

# Build:
cmake --build . -j <num jobs>   # invokes make (or ninja, etc)

# Run tests and examples:
ctest

See CMake Options for details on customizing the build.

Create a Development Branch

All work should be done in a development branch (also called a "topic branch") and not directly in the master branch. This makes it easier to manage multiple in-progress patches at once, and provides a descriptive label for your patch as it passes through the review system.

To create a new branch based on the current master:

# Checkout local master branch:
cd /path/to/cub/sources
git checkout master

# Sync local master branch with github:
git pull

# Create a new branch named `my_descriptive_branch_name` based on master:
git checkout -b my_descriptive_branch_name

# Verify that the branch has been created and is currently checked out:
git branch

CUB branch names should follow a particular pattern:

  • For new features, name the branch feature/<name>
  • For bugfixes associated with a github issue, use bug/github/<bug-description>-<bug-id>
    • Internal nvidia and gitlab bugs should use nvidia or gitlab in place of github.

Local Development Loop

Edit, Build, Test, Repeat

Once the topic branch is created, you're all set to start working on CUB code. Make some changes, then build and test them:

# Implement changes:
cd /path/to/cub/sources
emacs cub/some_file.cuh # or whatever editor you prefer

# Create / update a unit test for your changes:
emacs tests/some_test.cu

# Check that everything builds and tests pass:
cd /path/to/cub/build/directory
cmake --build . -j <num_jobs> # or make, ninja, etc
ctest

Creating a Commit

Once you're satisfied with your patch, commit your changes:

# Manually add changed files and create a commit:
cd /path/to/cub
git add cub/some_file.cuh
git add tests/some_test.cu
git commit

# Or, if possible, use git-gui to review your changes while building your patch:
git gui

Writing a Commit Message

Your commit message will communicate the purpose and rationale behind your patch to other developers, and will be used to populate the initial description of your Github pull request.

When writing a commit message, the following standard format should be used, since tools in the git ecosystem are designed to parse this correctly:

First line of commit message is a short summary (<80 char)
<Second line left blank>
Detailed description of change begins on third line. This portion can
span multiple lines, try to manually wrap them at something reasonable.

Blank lines can be used to separate multiple paragraphs in the description.

If your patch is associated with another pull request or issue in the main
CUB repository, you should reference it with a `#` symbol, e.g.
#1023 for issue 1023.

For issues / pull requests in a different github repo, reference them using
the full syntax, e.g. thrust/thrust#4 for issue 4 in the thrust/thrust repo.

Markdown is recommended for formatting more detailed messages, as these will
be nicely rendered on Github, etc.

Push Development Branch to your Fork

Once you've committed your changes to a local development branch, it's time to push them to your fork:

cd /path/to/cub/checkout
git checkout my_descriptive_branch_name # if not already checked out
git push --set-upstream github-fork my_descriptive_branch_name

--set-upstream github-fork tells git that future pushes/pulls on this branch should target your github-fork remote by default.

Create Pull Request

To create a pull request for your freshly pushed branch, open your github fork in a browser by going to https://www.github.com/<GITHUB_USERNAME>/cub. A prompt may automatically appear asking you to create a pull request if you've recently pushed a branch.

If there's no prompt, go to "Code" > "Branches" and click the appropriate "New pull request" button for your branch.

If you would like a specific developer to review your patch, feel free to request them as a reviewer at this time.

The CUB team will review your patch, test it on NVIDIA's internal CI, and provide feedback.

Address Feedback and Update Pull Request

If the reviewers request changes to your patch, use the following process to update the pull request:

# Make changes:
cd /path/to/cub/sources
git checkout my_descriptive_branch_name
emacs cub/some_file.cuh
emacs tests/some_test.cu

# Build + test
cd /path/to/thrust/build/directory
cmake --build . -j <num jobs>
ctest

# Amend commit:
cd /path/to/cub/sources
git add cub/some_file.cuh
git add tests/some_test.cu
git commit --amend
# Or
git gui # Check the "Amend Last Commit" box

# Update the branch on your fork:
git push -f

At this point, the pull request should show your recent changes.

When Your PR is Approved

Once your pull request is approved by the CUB team, no further action is needed from you. We will handle integrating it since we must coordinate changes to master with NVIDIA's internal perforce repository.

CMake Options

A CUB build is configured using CMake options. These may be passed to CMake using

cmake -D<option_name>=<value> /path/to/cub/sources

or configured interactively with the ccmake or cmake-gui interfaces.

The configuration options for CUB are:

  • CMAKE_BUILD_TYPE={Release, Debug, RelWithDebInfo, MinSizeRel}
    • Standard CMake build option. Default: RelWithDebInfo
  • CUB_ENABLE_HEADER_TESTING={ON, OFF}
    • Whether to test compile public headers. Default is ON.
  • CUB_ENABLE_TESTING={ON, OFF}
    • Whether to build unit tests. Default is ON.
  • CUB_ENABLE_EXAMPLES={ON, OFF}
    • Whether to build examples. Default is ON.
  • CUB_ENABLE_DIALECT_CPPXX={ON, OFF}
    • Toggle whether a specific C++ dialect will be targeted.
    • Multiple dialects may be targeted in a single build.
    • Possible values of XX are {11, 14, 17}.
    • By default, only C++14 is enabled.
  • CUB_ENABLE_COMPUTE_XX={ON, OFF}
    • Controls the targeted CUDA architecture(s)
    • Multiple options may be selected when using NVCC as the CUDA compiler.
    • Valid values of XX are: {35, 37, 50, 52, 53, 60, 61, 62, 70, 72, 75, 80}
    • Default value depends on CUB_DISABLE_ARCH_BY_DEFAULT:
  • CUB_ENABLE_COMPUTE_FUTURE={ON, OFF}
    • If enabled, CUDA objects will target the most recent virtual architecture in addition to the real architectures specified by the CUB_ENABLE_COMPUTE_XX options.
    • Default value depends on CUB_DISABLE_ARCH_BY_DEFAULT:
  • CUB_DISABLE_ARCH_BY_DEFAULT={ON, OFF}
    • When ON, all CUB_ENABLE_COMPUTE_* options are initially OFF.
    • Default: OFF (meaning all architectures are enabled by default)
  • CUB_ENABLE_TESTS_WITH_RDC={ON, OFF}
    • Whether to enable Relocatable Device Code when building tests. Default is OFF.
  • CUB_ENABLE_EXAMPLES_WITH_RDC={ON, OFF}
    • Whether to enable Relocatable Device Code when building examples. Default is OFF.

Development Model

The following is a description of the basic development process that CUB follows. This is a living document that will evolve as our process evolves.

CUB is distributed in three ways:

  • On GitHub.
  • In the NVIDIA HPC SDK.
  • In the CUDA Toolkit.

Trunk Based Development

CUB uses trunk based development. There is a single long-lived branch called master. Engineers may create branches for feature development. Such branches always merge into master. There are no release branches. Releases are produced by taking a snapshot of master ("snapping"). After a release has been snapped from master, it will never be changed.

Repositories

As CUB is developed both on GitHub and internally at NVIDIA, there are three main places where code lives:

  • The Source of Truth, the public CUB repository, referred to as github later in this document.
  • An internal GitLab repository, referred to as gitlab later in this document.
  • An internal Perforce repository, referred to as perforce later in this document.

Versioning

CUB has its own versioning system for releases, independent of the versioning scheme of the NVIDIA HPC SDK or the CUDA Toolkit.

Today, CUB version numbers have a specific semantic meaning. Releases prior to 1.10.0 largely, but not strictly, followed these semantic meanings.

The version number for a CUB release uses the following format: MMM.mmm.ss-ppp, where:

  • CUB_VERSION_MAJOR/MMM: Major version, up to 3 decimal digits. It is incremented when the fundamental nature of the library evolves, leading to widespread changes across the entire library interface with no guarantee of API, ABI, or semantic compatibility with former versions.
  • CUB_VERSION_MINOR/mmm: Minor version, up to 3 decimal digits. It is incremented when breaking API, ABI, or semantic changes are made.
  • CUB_VERSION_SUBMINOR/ss: Subminor version, up to 2 decimal digits. It is incremented when notable new features or bug fixes or features that are API, ABI, and semantic backwards compatible are added.
  • CUB_PATCH_NUMBER/ppp: Patch number, up to 3 decimal digits. It is incremented if any change in the repo whatsoever is made and no other version component has been incremented.

The <cub/version.h> header defines CUB_* macros for all of the version components mentioned above. Additionally, a CUB_VERSION macro is defined, which is an integer literal containing all of the version components except for CUB_PATCH_NUMBER.

Branches and Tags

The following tag names are used in the CUB project:

  • github/nvhpc-X.Y: the tag that directly corresponds to what has been shipped in the NVIDIA HPC SDK release X.Y.
  • github/cuda-X.Y: the tag that directly corresponds to what has been shipped in the CUDA Toolkit release X.Y.
  • github/A.B.C: the tag that directly corresponds to a CUB version A.B.C.

The following branch names are used in the CUB project:

  • github/master: the Source of Truth development branch of CUB.
  • github/old-master: the old Source of Truth branch, before unification of public and internal repositories.
  • github/feature/<name>: feature branch for a feature under development.
  • github/bug/<bug-system>/<bug-description>-<bug-id>: bug fix branch, where bug-system is github or nvidia.
  • gitlab/master: mirror of github/master.
  • perforce/private: mirrored github/master, plus files necessary for internal NVIDIA testing systems.

On the rare occasion that we cannot do work in the open, for example when developing a change specific to an unreleased product, these branches may exist on gitlab instead of github. By default, everything should be in the open on github unless there is a strong motivation for it to not be open.