Allen: A high level trigger on GPUs for LHCb

TL;DR

Allen is a GPU-based first level trigger system for LHCb that processes 40 Tbit/s data, performs complex pattern recognition, and operates at full collision rate using around 500 GPUs, marking a first in high-throughput GPU triggers for HEP.

Contribution

This paper introduces Allen, the first complete high-throughput GPU trigger system for a HEP experiment, capable of handling the full data rate of LHCb's upgrade.

Findings

Processes 40 Tbit/s data rate in real-time

Operates at 30 MHz collision rate

Uses around 500 GPUs for full operation

Abstract

We describe a fully GPU-based implementation of the first level trigger for the upgrade of the LHCb detector, due to start data taking in 2021. We demonstrate that our implementation, named Allen, can process the 40 Tbit/s data rate of the upgraded LHCb detector and perform a wide variety of pattern recognition tasks. These include finding the trajectories of charged particles, finding proton-proton collision points, identifying particles as hadrons or muons, and finding the displaced decay vertices of long-lived particles. We further demonstrate that Allen can be implemented in around 500 scientific or consumer GPU cards, that it is not I/O bound, and can be operated at the full LHC collision rate of 30 MHz. Allen is the first complete high-throughput GPU trigger proposed for a HEP experiment.