Operational Intelligence in the ATLAS Continuous Integration System

The ATLAS Continuous Integration (CI) System is the major component of the ATLAS software development infrastructure, synchronizing efforts of several hundred software developers working around the world and around the clock. Powered by 700 fast processors, it is based on the ATLAS GitLab code management service and Jenkins CI server and performs daily up to 100 ATLAS software builds probing the code changes proposed in merge requests. The system uses Operational Intelligence methods to shorten development cycles and lower operating costs. The paper describes these methods, such as removal of redundant operations, compilation and testing parallelization, usage of directed acyclic graph (DAG) approach in CI pipelines as well as reports achieved improvements.