Buildroot:Top Level Parallel Build

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This page documents the effort to support top-level parallel build in Buildroot.

Core support

The core support for top-level parallel build was merged, is currently in master, and will be part of the 2020.02 release. What was merged is essentially:

  • Per-package directory support, through the BR2_PER_PACKAGE_DIRECTORIES option
  • Ability to do top-level parallel build using make -jX, when BR2_PER_PACKAGE_DIRECTORIES=y

Per-package directory fixes

All the fixes that we currently have are available at This branch is regularly rebased.

  • Issues with Python modules
    • Need to rewrite before building a Python module. PENDING until the core support is merged. It is fixed by package/pkg-python: fix for per-package directories
  • Issues with Meson packages
  • Issues with apr/apr-util/apache packages
    • These issues are fixed by a number of fixups. PENDING until the core support is merged. It is fixed by package/apr-util: fix build with per-package directories and package/apache: fix build with per-package directory support in our branch.
  • Issue with the owfs package
    • Needs a fixup. PENDING until the core support is merged. It is fixed by package/owfs: fixup Python sysconfigdata for per-package directories in our branch.

Known remaining issues

  • The Qt5 packages are broken with per-package directory support. See the thread at for details.
  • The build-time.log file is appended concurrently by multiple packages, probably not good.
  • The package-file-list*.txt files are appended concurrently by multiple packages, probably not good.
  • Some kconfig packages do not have a proper dependency on ccache if ccache support is enabled. This is however not strictly speaking a per-package directory issue.


To test top-level parallel-build:

  1. Grab the current master branch
  2. Enable BR2_PER_PACKAGE_DIRECTORIES in your Buildroot configuration
  3. Run your build with make -jX

Note that the output will be garbled, as the output of multiple packages building in parallel will be mixed together. You can decide to build with make -jX --output-sync=target to have a cleaner output.

Autobuilder testing

The autobuilders are already testing BR2_PER_PACKAGE_DIRECTORIES and top-level parallel build:

  • 1 build out of 15 build is built with BR2_PER_PACKAGE_DIRECTORIES
  • When BR2_PER_PACKAGE_DIRECTORIES=y, one out of two builds is built in top-level parallel build mode

The build results with BR2_PER_PACKAGE_DIRECTORIES=y is available at


This is only available in the ppsh-v8-work branch mentioned above, and not in master.

To visualize how well (or not so well) your build is parallelized, you can run at the end of a clean build:

  1. make graph-build-time
  2. evince output/graphs/build.timeline.pdf