CERN Accelerating science

ATLAS Note
Report number	ATL-DAQ-PROC-2019-017
Title	Implementation of the ATLAS trigger within the multi-threaded AthenaMT framework
Author(s)	Elliot, Alison (Queen Mary University of London) ; ATLAS Collaboration
Corporate Author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Publication	2019
Imprint	14 Sep 2019
Number of pages	4
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	Trigger ; Athena ; AthenaMT
Abstract	Athena is the software framework used in the ATLAS experiment throughout the data process- ing path, from the software trigger system through offline event reconstruction to physics analy- sis. The shift from high-power single-core CPUs to multi-core systems in the computing market means that the throughput capabilities of the framework have become limited by the available memory per process. For Run 2 of the Large Hadron Collider (LHC), ATLAS has exploited a multi-process forking approach with the copy-on-write mechanism to reduce the memory use. To better match the increasing CPU core count and the, therefore, decreasing available memory per core, a multi-threaded framework, AthenaMT, has been designed and is now being implemented. The ATLAS High Level Trigger (HLT) system has been remodelled to fit the new framework and to rely on common solutions between online and offline software to a greater extent than in Run 2. Presented is the implementation of the new HLT system within the AthenaMT framework, which will be used in ATLAS data-taking during Run 3 (2021-2023) of the LHC.