Diagnostic systems and resource utilization of the ATLAS high level trigger

With the first year of successful data taking of proton-proton collisions at LHC, the full chain of the ATLAS Trigger and Data Acquisition System could be tested under real conditions. The trigger monitoring and data quality infrastructure was essential to this success. We describe the software tools used to monitor the trigger system performance, assess the overall quality of the trigger selection and analyze the resource utilization during collision runs. Monitoring the performance and operation of these systems required smooth and parallel running of many complex software tools depending on each other. These are the basis for rate measurements, data quality determination of selected objects and supervision of the system during the data taking. Based on the data taking experience with first collisions, we describe the ATLAS trigger monitoring and operations performance.