Optimization of opportunistic utilization of the ATLAS high-level trigger farm for LHC Run 3

The ATLAS Trigger and Data Acquisition (TDAQ) High Level Trigger (HLT) computing farm contains 120 000 CPU cores. These resources are critical for the online selection and collection of collision data in the ATLAS experiment during LHC operation. Since 2013, during a longer period of LHC inactivity, these resources are being used for offline event simulation via the “Simulation at Point One” project (Sim@P1). With the recent start of LHC Run 3 and the flat computing budget expected in the near future, finding ways to maximize resource utilization efficiency is of paramount importance. Recent improvements in the ATLAS software stack can potentially allow the utilization of the Sim@P1 even during LHC operation for the duration of the LHC inter-fill gaps. While previous papers on the Sim@P1 project emphasized the technical implementation details, the current contribution is presenting results of a variety of tests that led to the optimal configuration of the job submission infrastructure which would allow the use of Sim@P1 during LHC Run 3.