SIMD studies in the LHCb reconstruction software

21st International Conference on Computing in High Energy and Nuclear Physics

物理学;计算机科学

Pérez, Daniel Hugo Cámpora^1 ; Couturier, Ben^1

CERN, PH Department, Geneva, Switzerland^1

关键词: Concurrent execution;    Functional units;    Online computing;    Programming paradigms;    Reconstruction algorithms;    Reconstruction software;    Single instruction multiple data;    Stringent requirement;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/664/9/092004/pdf
DOI  :  10.1088/1742-6596/664/9/092004

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

During the data taking process in the LHC at CERN, millions of collisions are recorded every second by the LHCb Detector. The LHCb Online computing farm, counting around 15000 cores, is dedicated to the reconstruction of the events in real-time, in order to filter those with interesting Physics. The ones kept are later analysed Offline in a more precise fashion on the Grid. This imposes very stringent requirements on the reconstruction software, which has to be as efficient as possible. Modern CPUs support so-called vector-extensions, which extend their Instruction Sets, allowing for concurrent execution across functional units. Several libraries expose the Single Instruction Multiple Data programming paradigm to issue these instructions. The use of vectorisation in our codebase can provide performance boosts, leading ultimately to Physics reconstruction enhancements. In this paper, we present vectorisation studies of significant reconstruction algorithms. A variety of vectorisation libraries are analysed and compared in terms of design, maintainability and performance. We also present the steps taken to systematically measure the performance of the released software, to ensure the consistency of the run-time of the vectorised software.