Compass SPMD: a SPMD vectorized tracking algorithm

Abstract

Compass is a SPMD (Single Program Multiple Data) tracking algorithm for the upcoming LHCb upgrade in 2021. 40 Tb/s need to be processed in real-time to select events. Alternative frameworks, algorithms and architectures are being tested to cope with the deluge of data. Allen is a research and development project aiming to run the full HLT1 (High Level Trigger) on GPUs (Graphics Processing Units). Allen’s architecture focuses on data-oriented layout and algorithms to better exploit parallel architectures. GPUs already proved to exploit the framework efficiently with the algorithms developed for Allen, implemented and optimized for GPU architectures. We explore opportunities for the SIMD (Single Instruction Multiple Data) paradigm in CPUs through the Compass algorithm. We use the Intel SPMD Program Compiler (ISPC) to achieve good readability, maintainability and performance writing “GPU-like” source code, preserving the main design of the algorithm.