Abstract

Event data from proton-proton collisions at the LHC will be selected by the ATLAS experiment in a three-level trigger system, which, at its first two trigger levels (LVL1+LVL2), reduces the initial bunch crossing rate of 40 MHz to ~ 3 kHz. At this rate, the Event Builder collects the data from the readout system PCs (ROSs) and provides fully assembled events to the Event Filter (EF). The EF is the third trigger level and its aim is to achieve a further rate reduction to ~ 200 Hz on the permanent storage. The Event Builder is based on a farm of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (100) PCs, interconnected via a gigabit Ethernet to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> (150) ROSs. These PCs run Linux and multi-threaded software applications implemented in C++. All the ROSs, and substantial fractions of the Event Builder and EF PCs have been installed and commissioned. We report on performance tests on this initial system, which is capable of going beyond the required data rates and bandwidths for event building for the ATLAS experiment.

Highlights

  • – receives trigger via the network – assigns events to the SFIs, load balancing the farm – handles End­Of­Event – sends clear messages to the ROSes

  • 1/3 of the ATLAS Event Builder nodes are installed and tested ATLAS Event builder is based on a pull protocol

  • – 15% degradation running two applications on a single node instead of two – still able to provide more than needed throughput per application

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Summary

19 ROS concentrator

SFI/DFM: dual AMD Opteron 252 2.6 GHz HLT: dual Intel Xeon E5320 quad­core 1.86GHz. Extend test capabilities running SFI application on HLT nodes Perfect scaling up to 59 SFIs. – 1.5 MB event size – 6.5GB/s @ 4.5kHz SFI application can roughly exploit the full GE link – 114MB/s @ 76 Hz (SFI) – 112MB/s @ 75 Hz (HLT) Multi­core HLT nodes have good SFI performance – Double SFI approach Very promising result, BUT. – dual­CPU quad­core 1.86GHz – 2 bonded interfaces toward ROSes – 2 bonded interfaces toward the EF Throughput with 32 ROSes, 1.1 MB event – Reference SFI 95 MB/s – Double SFI 2 x 80 MB/s = 160 MB/s Good performance, limited by the (output) bonding efficiency – Input only: 2 x 114 MB/s = 228 MB/s – Foreseen working point

Conclusions
12 DFM PCs installed
Full Text
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