Teach gn to handle systems with > 64 processors

Previously, when run on Windows systems with > 64 logical processors,
gn's calculation of the number of available processors (used to
determine how many worker threads to create) under-counted the number of
processors, thereby not making full use of the system's available
processing power.

This change corrects gn's count of available CPUs so that it can use all
of the system's processors. In addition to creating the correct number
of workers, this change also distributes created workers between
processor groups, a necessary step when utilizing more than 64
processors on Windows.

On the 72-logical-processor P920, this change makes gn gen use all 36
cores, rather than only 18.

Bug: crbug.com/982982
Change-Id: I40b40f4d34b634566991e4bebf686f48836445e8
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/5660
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
2 files changed
tree: 1f9c768a90c67c3c3b5ecaf09f426e7d0fbe1dda
  1. base/
  2. build/
  3. docs/
  4. examples/
  5. infra/
  6. tools/
  7. util/
  8. .clang-format
  9. .editorconfig
  10. .gitignore
  11. .style.yapf
  14. OWNERS
  15. README.md


GN is a meta-build system that generates build files for Ninja. There is documentation in docs/ and a presentation on it.

Getting a binary

You can download the latest version of GN binary for Linux, macOS and Windows.

Alternatively, you can build GN from source:

git clone https://gn.googlesource.com/gn
cd gn
python build/gen.py
ninja -C out
# To run tests:

On Windows, it is expected that cl.exe, link.exe, and lib.exe can be found in PATH, so you'll want to run from a Visual Studio command prompt, or similar.

On Linux and Mac, the default compiler is clang++, a recent version is expected to be found in PATH. This can be overridden by setting CC, CXX, and AR.


There is a simple example in examples/simple_build directory that is a good place to get started with the minimal configuration.

For a maximal configuration see the Chromium setup:

and the Fuchsia setup:

Reporting bugs

If you find a bug, you can see if it is known or report it in the bug database.

Sending patches

GN uses Gerrit for code review. The short version of how to patch is:

Register at https://gn-review.googlesource.com.

... edit code ...
ninja -C out && out/gn_unittests

Then, to upload a change for review:

git commit
git cl upload --gerrit

When revising a change, use:

git commit --amend
git cl upload --gerrit

which will add the new changes to the existing code review, rather than creating a new one.

We ask that all contributors sign Google's Contributor License Agreement (either individual or corporate as appropriate, select ‘any other Google project’).


You may ask questions and follow along with GN‘s development on Chromium’s gn-dev@ Google Group.