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To MEP or not to MEP

To MEP or not to MEP. Niko Neufeld RTTC meeting, October 26th 2004. The LHCb transport format: MEPs. The online transport format is MEPs: https://edms.cern.ch/document/499933.1

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To MEP or not to MEP

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  1. To MEP or not to MEP Niko Neufeld RTTC meeting, October 26th 2004

  2. The LHCb transport format: MEPs • The online transport format is MEPs:https://edms.cern.ch/document/499933.1 • MEP means that event fragments from several consecutive triggers are merged into one MEP and send as a single IPv4 packet • MEPs are used in HLT and L1 to reduce the overhead incurred by sending small packets over the network • The number of fragments in a MEP is called the packing factor (PF) - it is a constant (during a run), adjustable global parameter of the system • The nominal PFs for L1 and HLT are 25 and 10 respectively Niko Neufeld CERN, PH

  3. Sending Events in the RTTC • In the RTTC we will have a single source of data (a disk-server) sending to at least one sub-farm (most likely three) • This means we could send completely build events to the SFC and the SFC would just “forward” them • I think we should not opt for this strategy Niko Neufeld CERN, PH

  4. Fully realistic event-builder in action with all timing relevant overheads, packet handling issues No special version of event-builder code Possibility to much more realistic robustness tests (missing/corrupted MEP from single source will be the most likely error in the final system) Need to reformat raw data into MEPs: not difficult, study in progress, will present results in next meeting Need real event-builder: no problem: will be tested and ready by end of this year (c.f. Benjamin’s talk) sub-farms will not run at 120 MB/s --> even a less performing SFC can do the job The case for MEPs Niko Neufeld CERN, PH

  5. “To MEP or not to MEP, that is the question here” • I think, “’Tis MEPness, but there is a method in it” - or leaving Shakespeare aside: • For the price of a few technical details (re-formatting of raw-data) we get a fully realistic system - we should go for MEPs Niko Neufeld CERN, PH

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