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September 2021

KernelCI Hackfests

By Blog, Community

KernelCI hackfests span over a few days during which a number of contributors get together to focus on upstream Linux kernel testing. So far, mainly kernel and automated test system developers have been taking part in the hackfests but anyone is welcome to join. Topics mostly include extending test coverage in various ways: enabling new test suites as well as adding test cases to established frameworks such as kselftest and LTP, building additional kernel flavours, bringing up new types of hardware to be tested…

There have been two hackfests to date. The current plan is to hold one every few months. Future hackfests will be announced on the KernelCI mailing list as well as LKML and Twitter. Stay tuned!

Connecting the dots

There is a large ecosystem around the Linux kernel which includes testing in many shapes and forms: kernel developers, test developers, test system developers, OEMs testing fully integrated products… All these teams of people don’t necessarily interact with each other very much outside of their organisations, and kernel developers aren’t necessarily in the habit of writing tests as part of their daily work.

Events such as the KernelCI hackfests give a chance for people from these different areas to work together on solving common issues and keep the ecosystem healthy. It also helps with shifting the upstream Linux kernel development culture towards a more test-driven workflow, to bring mainline Linux closer to the real world where it is actually being used.

Let’s consider a plausible hackfest story. A first participant writes a new test, say in kselftest. A second participant enables the test to run in KernelCI, which fails in some cases and a kernel bug is found. A third participant makes a fix for the bug, which can then be tested directly in KernelCI to confirm it works as expected. This may even happen on the staging instance before the patches for the test and the fix are sent to any mailing list, in which case the fix would get a Tested-by: " bot" <> trailer from the start. This scenario also relies on some hardware previously made available in test labs by other people, putting together efforts from at least four different participants.


Here’s a summary of the first two hackfests:

Hackfest #1 – 27th May to 4th June 2021

  • Workboard:
  • Participans
    • Several kernel developers from Google Chrome OS
    • Several kernel developers from Collabora
    • A few members of the core KernelCI team
  • Achievements
    • New KernelCI instance for Chrome OS on
    • Added support for building Chrome OS configs on top of mainline
    • Enabled clang-13 builds for Chrome OS and main KernelCI builds
    • New test suite for libcamera enabled on
    • Enabled LTP crypto tests with extra kernel config fragment
    • Several patches were also sent to extend kselftest and KUnit coverage in the kernel tree

Hackfest #2 – 6th to 10th September 2021

Lessons Learned

What went well

  • There were several new contributors. The hackfest is a great way to get people started with KernelCI.
  • Hackfest #2 showed more diversity with a wider representation from the ecosystem.
  • There were many improvements in various areas (bug fixes, documentation) which is a sign of a healthy project.
  • The workflow based on GitHub and the Big Blue Button platform appear to have been easily adopted by the participants.

What needs to be improved

  • Having more kernel maintainers involved would help with setting priorities and ojectives for KernelCI in accordance with kernel developers’ needs.
  • A hackfest every 3 months may be a bit too often, or maybe some could be shorter or have a more particular theme.
  • Changes can take a long time to get merged. The main limitation seems to be the number of people available to do code reviews and drive discussions.
  • KernelCI has been focusing on running more tests for over a year (kselftest, LTP, IGT…). Now the core architecture needs to be improved to scale better.

Next hackfest

The actual dates haven’t been confirmed yet, but with the current 3-month frequency the next hackfest should be taking place early December 2021. A proposed theme could be “KernelCI for newbies”, with a selection of tasks well suited for first-time contributors and documentation improved in that area prior to the hackfest. As always, suggestions are always welcome so please do get in touch if you have any.

See you there!