High performance event-building in linux for LHCb

The LHCb experiment event-building is performed over a Gigabit Ethernet switched network. One specific step of event-building is implemented by a software running on a gateway PC whose role is to gather data packets from data sources, rebuild events and forward them to computing nodes for running trigger algorithms. In this article, we concentrate on the implementation of this component on a Linux system. While implementing the software, we made thorough studies of the kernel and profiled applications, leading to significant performance improvement. More importantly, these studies allowed us to also gain in terms of predictability thanks to a good understanding of the whole system. In this article, we use this application to illustrate possible improvements to system software for data acquisition. We describe in detail implementation choices and related operating system kernel code. These techniques and observations are generic enough to be applied to other similar systems.