Abstract
Estimations of the CPU resources that will be needed to produce simulated data for the future runs of the ATLAS experiment at the LHC, indicate a compelling need to speed-up the process to reduce the computational time required. While different fast simulation projects are ongoing, full Geant4 based simulation will still be heavily used and is expected to consume the biggest portion of the total estimated processing time. In order to run effectively on modern architectures and profit from multi-core designs a migration of the Athena framework to a multi-threading processing model was performed. A multi-threaded simulation based on AthenaMT and Geant4MT, enables substantial decreases in the memory footprint of jobs, largely from shared geometry and cross-section tables. This approach scales better with respect to the multi-processing approach (AthenaMP) especially on the architectures that are foreseen to be used in the next LHC runs. In these proceedings we report about the status of the multi-threaded simulation in ATLAS, focusing on the different challenges of its validation process. We demonstrate the different tools and strategies that have been used for debugging multi-threaded runs versus the corresponding sequential ones, in order to have a fully reproducible and consistent simulation result.
Highlights
IntroductionHigh-energy physics (HEP) experiments at the Large Hadron Collider (LHC) are preparing for the LHC runs that are respectively scheduled to start in 2021 (so called Run 3) and at the end of 2027 (so called Run 4 or High-Luminosity phase – HL-LHC), performing and planning major upgrades to their detectors
High-energy physics (HEP) experiments at the Large Hadron Collider (LHC) are preparing for the LHC runs that are respectively scheduled to start in 2021 and at the end of 2027, performing and planning major upgrades to their detectors
AthenaMT is based on GaudiHive, a multi-threaded, concurrent-execution extension to Gaudi [14]: its concurrency model is based on Intel R Threading Building Blocks library (TBB) [15] and the computation is broken down into tasks that can run in parallel
Summary
High-energy physics (HEP) experiments at the Large Hadron Collider (LHC) are preparing for the LHC runs that are respectively scheduled to start in 2021 (so called Run 3) and at the end of 2027 (so called Run 4 or High-Luminosity phase – HL-LHC), performing and planning major upgrades to their detectors. The increase in the intensity of the beam will allow for collisions where the average number of proton-proton interactions (pile-up) will increase from the current value of 60 to 200 All of this implies necessary changes to the detector hardware and software. These are compared to the projection (solid line) of what is expected to be available in a flat budget scenario that assumes an increase of 20% per year, in light of the technology trends at the start of 2018. One of the biggest project in which the ATLAS collaboration is concentrating its effort is the migration of the ATLAS software framework, Athena [7, 8] to a multi-threaded design
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