CERN Accelerating science

CMS Note
Report number	CMS-CR-2018-388
Title	The CMS event-builder system for LHC run 3 (2021-23)
Author(s)	Mommsen, Remigius (Fermilab) ; André, Jean-Marc (Fermilab) ; Behrens, Ulf (DESY) ; Branson, James (UC, San Diego) ; Brummer, Philipp (CERN ; KIT, Karlsruhe) ; Cittolin, Sergio (UC, San Diego) ; da Silva Gomes, Diego (CERN) ; Darlea, Georgiana-Lavinia (MIT) ; Deldicque, Christian (CERN) ; Demiragli, Zeynep (MIT) ; Dobson, Marc (CERN) ; Doualot, Nicolas (Fermilab) ; Erhan, Samim (UCLA) ; Fulcher, Jonathan (CERN) ; Gigi, Dominique (CERN) ; Gładki, Maciej (CERN) ; Glege, Frank (CERN) ; Gomez-Ceballos, Guillelmo (MIT) ; Hegeman, Jeroen (CERN) ; Holzner, André (UC, San Diego) ; Lettrich, Michael (CERN) ; Mečionis, Audrius (Fermilab ; Vilnius U. (main)) ; Meijers, Frans (CERN) ; Meschi, Emilio (CERN) ; Morović, Srećko (Fermilab) ; O'Dell, Vivian (Fermilab) ; Orsini, Luciano (CERN) ; Papakrivopoulos, Ioannis (Natl. Tech. U., Athens) ; Paus, Christoph (MIT) ; Petrucci, Andrea (Rice U. (main)) ; Pieri, Marco (UC, San Diego) ; Rabady, Dinyar (CERN) ; Rácz, Attila (CERN) ; Rapševičius, Valdas (Fermilab ; Vilnius U. (main)) ; Reis, Thomas (CERN) ; Sakulin, Hannes (CERN) ; Schwick, Christoph (CERN) ; Šimelevičius, Dainius (CERN ; Vilnius U. (main)) ; Stankevičius, Mantas (Fermilab ; Vilnius U. (main)) ; Vazquez Velez, Cristina (CERN) ; Wernet, Christian (CERN) ; Zejdl, Petr (Fermilab ; CERN)
Publication	2019
Imprint	27 Nov 2018
Number of pages	8
In:	EPJ Web Conf. 214 (2019) 01006
In:	23rd International Conference on Computing in High Energy and Nuclear Physics, CHEP 2018, Sofia, Bulgaria, 9 - 13 Jul 2018, pp.01006
DOI	10.1051/epjconf/201921401006
Subject category	Detectors and Experimental Techniques
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	The data acquisition system (DAQ) of the CMS experiment at the CERN Large Hadron Collider (LHC) assembles events of 2 MB at a rate of100 kHz. The event builder collects event fragments from about 750 sources and assembles them into complete events which are then handed to the High-Level Trigger (HLT) processes running on $\mathcal{O}$(1000) computers. The aging event-building hardware will be replaced during the long shutdown 2 of the LHC taking place in 2019/20. The future data networks will be based on 100 Gb/s interconnects using Ethernet and Infiniband technologies. More powerful computers may allow to combine the currently separate functionality of the readout and builder units into a single I/O processor handling simultaneously 100 Gb/s of input and output traffic. It might be beneficial to preprocess data originating from specific detector parts or regions before handling it to generic HLT processors. Therefore, we will investigate how specialized coprocessors, e.g. GPUs, could be integrated into the event builder. We will present the envisioned changes to the event-builder compared to today’s system. Initial measurements of the performance of the data networks under the event-building traffic pattern will be shown. Implications of a folded network architecture for the event building and corresponding changes to the software implementation will be discussed.
Copyright/License	publication: © 2019-2025 The Authors (License: CC-BY-4.0)

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