[Mesa-dev] Mesa CI with trace regression testing

[Alexandros Frantzis]

Hi all,

The last couple of months we (at Collabora) have been working on a
prototype for a Mesa testing system based on trace replays that supports
correctness regression testing and, in the future, performance
regression testing.

We are aware that large-scale CI systems that perform extensive checks
on Mesa already exist. However, our goal is not to reach that kind of
scale or exhaustiveness, but to produce a system that will be simple and
robust enough to be maintained by the community, while being useful
enough so that the community will want to use and maintain it. We also
want to be able to make it fast enough so that it will be run eventually
on a regular basis, ideally in pre-commit fashion.

The current prototype focuses on the correctness aspect, replaying
traces and comparing images against a set of reference images on
multiple devices. At the moment, we run on softpipe and
intel/chromebook, but it's straightforward to add other devices through
gitlab runners.

For the prototype we have used a simple approach for image comparison,
storing a separate set of reference images per device and using exact
image comparison, but we are also investigating alternative ways to deal
with this. First results indicate that the frequency of reference image
mismatches due to non-bug changes in Mesa is acceptable, but we will get
a more complete picture once we have a richer set of traces and a longer
CI run history. 

The current design is based on an out-of-tree approach, where the tracie
CI works independently from Mesa CI, fetching and building the latest
Mesa on its own. We did this for maximum flexibility in the prototyping
phase, but this has a complexity cost, and although we could continue to
work this way, we would like to hear people's thoughts about eventually
integrating with Mesa more closely, by becoming part of the upstream
Mesa testing pipelines.

It's worth noting that the last few months other people, most notably
Eric Anholt, have made proposals to extend the scope of testing in CI.
We believe there is much common ground here (multiple devices,
deployment with gitlab runners) and room for cooperation and eventual
integration into upstream Mesa. In the end, the main difference between
all these efforts are the kind of tests (deqp, traces, performance) that
are being run, which all have their place and offer different
trade-offs.

We have also implemented a prototype dashboard to display the results,
which we have deployed at:

https://tracie.freedesktop.org

We are working to improve the dashboard and provide more value by
extracting and displaying additional information, e.g., "softpipe broken
since commit NNN".

The dashboard is currently specific to the trace playback results, but
it would be nice to eventually converge to a single MesaCI dashboard
covering all kinds of Mesa CI test results. We would be happy to help
develop in this direction if there is interest.

You can find the CI scripts for tracie at:

https://gitlab.freedesktop.org/gfx-ci/tracie/tracie

Code for the dashboard is at:

https://gitlab.freedesktop.org/gfx-ci/tracie/tracie_dashboard

Here is an example of a failed CI job (for a purposefully broken Mesa
commit) and the report of the failed trace (click on the red X to
see the image diffs):

https://tracie.freedesktop.org/dashboard/job/642369/

Looking forward to your thoughts and comments.

Thanks,
Alexandros