CERN Accelerating science

ATLAS Slides
Report number	ATL-SOFT-SLIDE-2018-429
Title	I/O in the ATLAS multithreaded framework
Author(s)	Cranshaw, Jack (Argonne National Laboratory) ; Malon, David (Argonne National Laboratory) ; Nowak, Marcin (Brookhaven National Laboratory (BNL)) ; Van Gemmeren, Peter (Argonne National Laboratory)
Corporate author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Submitted by	[email protected] on 30 Jun 2018
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Abstract	Scalable multithreading poses challenges to I/O, and the performance of a thread-safe I/O strategy may depend upon many factors, including I/O latencies, whether tasks are CPU- or I/O-intensive, and thread count. In a multithreaded framework, an I/O infrastructure must efficiently supply event data to and collect it from many threads processing multiple events in flight. In particular, on-demand reading from multiple threads may challenge caching strategies that were developed for serial processing and may need to be enhanced. This I/O infrastructure must also address how to read, make available, and propagate in-file metadata and other non-event data needed as context for event processing. We describe the design and scheduling of I/O components in the ATLAS multithreaded control framework, AthenaMT, for both event and non-event I/O. We discuss issues associated with exploiting the multithreading capabilities of our underlying persistence technology, ROOT, in a manner harmonious with the ATLAS framework’s own approach to thread management. Finally, we discuss opportunities for evolution and simplification of I/O components that have successfully supported ATLAS event processing for many years from their serial incarnations to their thread-safe counterparts.