1. Network Architecture for the LHCb DAQ Upgrade Guoming Liu CERN, Switzerland Upgrade DAQ Miniworkshop May 27, 2013

2.  Introduction to the LHCb DAQ Upgrade: numbers  Potential network technologies for the DAQ upgrade  DAQ network architecture  DAQ schemes  Summary 2 Outlines

3.  Timeframe: installation in the second long shut-down of the LHC in 2018, be ready for data taking in 2019  Trigger: a fully flexible software solution.  Low Level Trigger (LLT) : tune the input rate to the computing farm from 1 – 40 MHz when the system is not fully ready for 40 MHz  The DAQ system should be capable of reading out the whole detector at the LHC collision rate of 40MHz.  Numbers for the DAQ Network  Event size: ~100 KB  Max. event input rate: 40 MHz  Unidirectional Bandwidth: ~38.4 Tbit/s (may scale up) 3 LHCb DAQ Upgrade

4.  High-speed interconnection technologies  Ethernet (10G/40G/00G)  InfiniBand (FDR, coming EDR)  Some other similar technologies  Ethernet  Very popular for desktop/station/server  Familiar by users/developers  InfiniBand  Mainly used in high performance computing and large enterprise data center  High speed: 56Gb/s FDR  Great performance/price 4 Network Technologies

5. 5 Ethernet vs InfiniBand EthernetInfiniBand ReliabilityBest effort, relies on upper layer protocol TCP/IP Hardware based re- transmission Flow ControlPause frame, temporarily blocking the transmission Credit based Switch MethodStore-and-forward or cut- through Cut-through Buffer sizeLarge (store-and-forward) or small (cut-through) Small

6.  Readout board (TELL1): custom FPGA board  UDP-like transport protocol: MEP (Multi- Event Packet)  Push DAQ scheme  Deep buffer is required in the routers and the switches 6 Review: Current LHCb DAQ Evt m Frag. Evt m Frag. Evt m Frag. CPU n: DataReq Evt m, Dest n Evt m, Dest n Evt m, Dest n

7.  Unidirectional solution:  Dataflow in the core network is unidirectional  Bidirectional mixed solution:  Readout Unit (RU) & Builder Unit (BU) connected to the same Top-Of-Rack (TOR) switch, dataflow in the core network is bidirectional  Bidirectional uniform solution:  RU & BU combined in the same server, dataflow in the core network is bidirectional 7 Network Architecture for DAQ upgrdae

8.  All the readout units are connected to the core network  The builder unit and the filter unit are implemented in the same server.  The dataflow in the core network is unidirectional 8 Unidirectional solution

9. 9 DAQ: Core Network Monolithic core router fabric with fat-tree topologyvs

10.  Monolithic core-router (current solution in LHCb)  pros: “simple” architecture, good performance  cons: expensive, not many choices  Fabric with fat-tree topology : many small Top-of-Rack (TOR) switches  pros: cost-efficiency, scalability, flexibility  cons: complexity  Fabric is quite popular in data center: Cisco FabricPath, Juniper QFabri, and also other large chassis … 10 Ethernet vs InfiniBand

11.  The builder unit and the filter unit are implemented in the same server  All the readout units are connected to the TOR switches instead of the core network. 11 Bidirectional mixed solution (1)

12.  The dataflow in the core network is bi-directional  Requires RUs and BU/FUs are close enough to connect the same TOR switch  This can save up to 50% of bandwidth and ports in the core network.  The price per port in the core network are usually 3 to 4 times more expensive than in a TOR switch 12 Bidirectional mixed solution (2)

13.  The readout unit and builder unit are implemented in the same server (RU/BU server)  The RU/BU server connects both the core network (for event building) and the TOR switch (for event filtering) 13 Bidirectional uniform solution (1)

14.  The dataflow in the core network is bi-directional  Saves up to 50% ports in the core network.  Possible to choose different network technologies for the core layer (event builder network) and the edge layer (event filter network).  e.g. cost-effective InfiniBand FDR for the core, low cost 10 GBase-T for the event filter network  Increases the flexibility: deep buffer, easy to implement different DAQ schemes in software  Not tied to any technology  Reduces the complexity in the FPGA receiver card  No deep buffer is needed  Simple protocol (e.g PCIe) with PC 14 Bidirectional uniform solution (2)

15.  Key to success of the uniform solution: the RU/BU module  RU/BU modules serve five purposes: 15 Bidirectional uniform solution (3)  Receives data fragments from the front-end electronics  Sends data fragments to the other modules  Builds complete events  Performs event filtering on a fraction of the complete events  Distributes the remaining events to a sub-farm of filter units 1234

16.  IO bandwidth requirements of RU/BU modules:  Full 24x GBT link  ~ 154 Gb/s input and output or ~ 215 Gb/s for wide user mode  Preliminary tests on a Sandy-Bridge server  Intel E5 2650: 2x16x2.0G  2x Mellanox dual-port InfiniBand FDR cards Connect-IB  OS: SLC 6.2  Software: MLNX-OFED 2.0  Connect-IB cards send and receive data simultaneously 16 Bidirectional uniform solution (4)

17.  Preliminary test results: input and output throughput  MLNX-OFED 2.0 is a beta version, but needed for the new dual-port cards  In MLNX-OFED 1.5.3, the throughput of the single-port card is close to the limit  More tunings on OS and software are needed to improve the performance 17 Bidirectional uniform solution (5)

18.  Several different DAQ schemes in term of the data flow  Push data without traffic shaping  Push data with barrel-shift traffic shaping  Pull data from the destinations  Different schemes fit for different network technologies and topologies  More details on Daniel’s talk later 18 DAQ schemes

19.  Both Ethernet and InfiniBand, or a mix of both can be the candidate for the DAQ network upgrade  Several architectures have been discussed, the uniform solution is the most flexible and cost-effective solution  Preliminary tests show the uniform solution can work  More studies for the LHCb DAQ network upgrade are needed, stay tuned for the development in industry 19 Summary

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