Published on October 17, 2007
The Data Flow System of the ATLAS DAQ/EF "-1" Prototype Project: The Data Flow System of the ATLAS DAQ/EF "-1" Prototype Project G. Ambrosini 3,9, E. Arik 2, H.P. Beck 1 , S. Cetin 2, T. Conka 2, A. Fernandes 3, D. Francis3, Y. Hasegawa 4, M. Joos 3, G. Lehmann 1,3 , J. Lopez 3,10, A. Mailov 2, L. Mapelli 3, G. Mornacchi 3, Y. Nagasaka7, M. Niculescu 3,5, K. Nurdan 2, J. Petersen 3, D. Prigent 3, J. Rochez 3, L. Tremblet3, G. Unel3 , S. Veneziano 3,6, Y. Yasu8 1. Laboratory for High Energy Physics, University of Bern, Switzerland 2. Department of Physics, Bogazici University, Istanbul, Turkey 3. CERN, Geneva, Switzerland 4. ICEPP, University of Tokio, Tokio, Japan 5. Institute of Atomic Physics,Bucharest, Romania 6. I.N.F.N. Sezione di Roma, Roma, Italy 7. Nagasaki Institute for Applied Science, Nagasaki, Japan 8. High Energy Accelerator Research Organization (KEK), Japan 9. Now at Lightning Instrumentation S.A., Lausanne, Switzerland 10. Now at EDF, Grenoble, France The DAQ/EF “-1” Project: The DAQ/EF “-1” Project Study of a vertical slice of the ATLAS DAQ system to: define requirements on different sub-systems, design the elements of the DAQ with their boundaries and their interaction with other components, implement a prototype to evaluate technological solutions with the requested performance. The project has been organized in 4 main activities: Detector interface Data Flow Event Filter Back-End (see talk by I. Soloviev on Thursday) View of the Data Flow System: View of the Data Flow System See talk by S. Veneziano Prototype Implementation of the Data Flow: Prototype Implementation of the Data Flow Global Performance Measurements: Global Performance Measurements ROB fragment size variable, with mean ~1.5 kBytes The EB dictates the performance for a L2 rejection ratio below 95% Measurements with no L2 rejection The performance is limited by the EB interface which collects fragments over VME and sends them out on the ATM network. The Event Builder (EB): The Event Builder (EB) The EB is responsible for merging data fragments to complete, formatted events The EB design is based on a two layer approach which separates the technology specific aspects from the functionality of the EB elements and their interaction protocol Bsy/NotBsy EoT Transfer EoE GetId Src DFM Dst The EB has been studied through prototyping and simulation EB Performance Measurements: Gigabit Ethernet : EB Performance Measurements: Gigabit Ethernet Processor: Intel Pentium PC @ 450 MHz OS: Linux Protocol: TCP/IP EB Performance Measurements: ATM: EB Performance Measurements: ATM Processor: RIOII 8062 SBC @ 200 MHz OS: LynxOS 2.5.1 Protocol: AAL5 ATM bandwidth Data Modelling of the EB: Modelling of the EB Main purpose: study of the scaling of the EB system performance to ATLAS sizes Model design: 2 layer approach as in the prototype in order to be capable of studying different technologies with the same model Simulation Program: implementation with the discrete event simulation domain of the PTOLEMY (http://ptolemy.eecs.berkeley.edu) simulation tool Network Node Scheme: Network Node Scheme Check queue Check queue Check User Buffer Send buffer queue Receive buffer queue C P U r u n n i n g t h e E B a p p l i c a t o n NIC NIC Flow of data Flow control: checking of queues and requesting data Every EB element is a network node. Only the application specific part distinguishes between DFM, EBIF and SFI. The Network is modelled as an ideal router introducing a constant delay between input and output. EB Scalability Studies: EB Scalability Studies The time to build an event increases fairly linearly with the number of EBIFs; nevertheless the data cannot exclude a weak quadratic dependency yet. ATM Scaling of the EB: Results of the simulation calibrated with the processing times and the ATM technology parameters measured in the prototype. The performance is strongly dependent on the evolution of the processing time as a function of the number of nodes. Scaling of the EB Link speed EB performance ATLAS region Scaling: Possible Improvements: Scaling: Possible Improvements Reduce the number of nodes in the system by introducing higher bandwidth links Increase the processing power of the nodes 400x400 ATM155 with 3 times faster CPU Conclusions: Conclusions An Event Builder prototype has been implemented for Gigabit Ethernet and ATM; the latter has been used to calibrate a computer model of the EB. The model shows that the EB design is scalable and that the required performance is in reach. A small but complete Data Flow prototype has been designed and implemented; a LVL2 accept rate of 2.3 kHz could be sustained for ROB fragment sizes of ~1.5 kBytes.