Vectorising the detector geometry to optimise particle transport

Abstract. The VecGeom geometry library is a relatively recent effort aiming to provide a modern and high performance geometry service for particle detector simulation in hierarchical detector geometries common to HEP experiments. One of its principal targets is the efficient use of vector SIMD hardware instructions to accelerate geometry calculations for single track as well as multi-track queries.Previously, excellent performance improvements compared to Geant4/ROOT could be reported for elementary geometry algorithms at the level of single shape queries. In this contribution, we will focus on the higher level navigation algorithms in VecGeom, which are the most important components as seen from the simulation engines. We will first report on our R&D effort and developments to implement SIMD enhanced data structures to speed up the well-known "voxelised" navigation algorithms, ubiquitously used for particle tracing in complex detector modules consisting of many daughter parts.Second, we will discuss complementary new approaches to improve navigation algorithms in HEP. These ideas are based on a systematic exploitation of static properties of the detector layout as well as automatic code generation and specialisation of the C++ navigator classes. Such specialisations reduce the overhead of generic-or virtual function based algorithms and enhance the effectiveness of the SIMD vector units.These novel approaches go well beyond the existing solutions available in Geant4 or TGeo/ROOT, achieve a significantly superior performance, and might be of interest for a wide range of simulation backends (GeantV, Geant4). We exemplify this with concrete benchmarks for the CMS and ALICE detectors.

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“…This work has been presented previously [10,11] and continues to be improved and extended constantly.…”

Section: Introductionmentioning

confidence: 85%

Accelerating navigation in the VecGeom geometry modeller

Wenzel

Zhang

Developers³

2017

J. Phys.: Conf. Ser.

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“…We therefore started the development of an optimised library for primitive solids and their compositions, and of the development of optimised algorithms for track navigation with API for both single-track and many-track queries. Starting from the USolids library [7], which was developed in the framework of the AIDA project, we have developed a high performance library (VecGeom) of geometrical routines with vector signature [8,9]. One example of the gain obtained with this new code can be seen in Figure 3.…”

Section: The Geometrymentioning

confidence: 99%

The GeantV project: preparing the future of simulation

Amádio

Apostolakis

Bandieramonte

et al. 2015

J. Phys.: Conf. Ser.

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Abstract. Detector simulation is consuming at least half of the HEP computing cycles, and even so, experiments have to take hard decisions on what to simulate, as their needs greatly surpass the availability of computing resources. New experiments still in the design phase such as FCC, CLIC and ILC as well as upgraded versions of the existing LHC detectors will push further the simulation requirements. Since the increase in computing resources is not likely to keep pace with our needs, it is therefore necessary to explore innovative ways of speeding up simulation in order to sustain the progress of High Energy Physics. The GeantV project aims at developing a high performance detector simulation system integrating fast and full simulation that can be ported on different computing architectures, including CPU accelerators. After more than two years of R&D the project has produced a prototype capable of transporting particles in complex geometries exploiting micro-parallelism, SIMD and multithreading. Portability is obtained via C++ template techniques that allow the development of machineindependent computational kernels. A set of tables derived from Geant4 for cross sections and final states provides a realistic shower development and, having been ported into a Geant4 physics list, can be used as a basis for a direct performance comparison.

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“…With both the improvement in network connection and the need for more dependent products, this scheme might be improved by replacing the copy by a reference to an external source, for example for the future update of the ROOT geometry package based on the VecGeom library [14]. This will require the development of strong, long lasting procedures to express and resolve the dependencies.…”

Section: Collaborationsmentioning

confidence: 99%