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HK: Fachverband Physik der Hadronen und Kerne

HK 55: Invited Talks V

HK 55.1: Hauptvortrag

Donnerstag, 31. März 2022, 11:00–11:30, HK-H1

Online data processing with GPUs in ALICE during LHC Run 3 — •David Rohr for the ALICE collaboration — CERN, Geneva, Switzerland

The ALICE experiment has undergone a major upgrade for LHC Run 3 and will record 50 times more heavy ion collisions than before. The new computing scheme for Run 3 replaces the traditionally separate online and offline frameworks by a unified one. Processing will happen in two phases. During data taking, a synchronous processing phase performs data compression, calibration, and quality control on the online computing farm. The output is stored on an on-site disk buffer. When there is no beam in the LHC, the same computing farm is used for the asynchronous reprocessing of the data which yields the final reconstruction output. ALICE will employ neither hardware nor software triggers for Pb-Pb data taking but instead store all collisions in compressed form. This requires full online processing of all recorded data, which is a major change compared to a traditional online systems, which sees only the data selected by a hardware trigger. To cope with the increased data rate and computing requirement, ALICE employs graphics cards (GPUs) as the backbone of the online processing. In order to make full use of the online farm also for asynchronous reconstruction, also a large fraction of the asynchronous phase is being designed to run on GPUs. The talk will detail the ALICE Run 3 computing scheme, and outline the hardware architecture and software design for synchronous and asynchronous processing.