Ensuring that top-of-trunk consistently generates high-quality code remains harder than it should be. Continuous integration (CI) setups that track correctness of top-of-trunk work pretty well today since they automatically report correctness regressions with low false positive rate to committers. In comparison, the output generated by CI setups that track performance require far more human effort to interpret.

In this talk, I’ll describe why I think effective performance tracking is hard and what problems need solving, with a focus on our real world experiences and observations.

As part of the bring-up of one of the public performance tracking bots, I’ve done an in-depth analysis of its performance and noise characteristics. The insights gained from this analysis drove a number of improvements to LNT and the test-suite in the past year. I hope that sharing these insights will help others in setting up low-noise performance-tracking bots.

I’ll conclude by summarizing what seem to be the most important missing pieces of CI functionality to make the performance-tracking infrastructure as effective as the correctness-tracking infrastructure.

This presentation has been given before at the US LLVM dev meeting in San Jose. Given the interest there and the mostly non-overlapping audience between the FOSDEM llvm dev room and the US dev meeting, I think it's worthwhile to repeat this presentation at FOSDEM.