Challenges and opportunities integrating LLAMA into AdePT

Particle transport simulations are a cornerstone of high-energy physics (HEP), constituting a substantial part of the computing workload performed in HEP. To boost the simulation throughput and energy efficiency, GPUs as accelerators have been explored in recent years, further driven by the increasing use of GPUs on HPCs. The Accelerated demonstrator of electromagnetic Particle Transport (AdePT) is an advanced prototype for offloading the simulation of electromagnetic showers in Geant4 to GPUs, and still undergoes continuous development and optimization. Improving memory layout and data access is vital to use modern, massively parallel GPU hardware efficiently, contributing to the challenge of migrating traditional CPU based data structures to GPUs in AdePT. The low-level abstraction of memory access (LLAMA) is a C++ library that provides a zero-runtime-overhead data structure abstraction layer, focusing on multidimensional arrays of nested, structured data. It provides a framework for defining and switching custom memory mappings at compile time to define data layouts and instrument data access, making LLAMA an ideal tool to tackle the memory-related optimization challenges in AdePT. Our contribution shares insights gained with LLAMA when instrumenting data access inside AdePT, complementing traditional GPU profiler outputs. We demonstrate traces of read/write counts to data structure elements as well as memory heatmaps. The acquired knowledge allowed for subsequent data layout optimizations

Increasing Parallelism in the ROOT I/O Subsystem

When processing large amounts of data, the rate at which reading and writing can take place is a critical factor. High energy physics data processing relying on ROOT is no exception. The recent parallelisation of LHC experiments' software frameworks and the analysis of the ever increasing amount of collision data collected by experiments further emphasized this issue underlying the need of increasing the implicit parallelism expressed within the ROOT I/O. In this contribution we highlight the improvements of the ROOT I/O subsystem which targeted a satisfactory scaling behaviour in a multithreaded context. The effect of parallelism on the individual steps which are chained by ROOT to read and write data, namely (de)compression, (de)serialisation, access to storage backend, are discussed. Performance measurements are discussed through real life examples coming from CMS production workflows on traditional server platforms and highly parallel architectures such as Intel Xeon Phi

Software Challenges For HL-LHC Data Analysis

The high energy physics community is discussing where investment is needed to prepare software for the HL-LHC and its unprecedented challenges. The ROOT project is one of the central software players in high energy physics since decades. From its experience and expectations, the ROOT team has distilled a comprehensive set of areas that should see research and development in the context of data analysis software, for making best use of HL-LHC's physics potential. This work shows what these areas could be, why the ROOT team believes investing in them is needed, which gains are expected, and where related work is ongoing. It can serve as an indication for future research proposals and cooperations

Eccentric strength assessment of hamstring muscles with new technologies: a systematic review of current methods and clinical implications

Background: Given the severe economic and performance implications of hamstring injuries, there are different attempts to identify their risk factors for subsequently developing injury prevention strategies to reduce the risk of these injuries. One of the strategies reported in the scientific literature is the application of interventions with eccentric exercises. To verify the effectiveness of these interventions, different eccentric strength measurements have been used with low-cost devices as alternatives to the widespread used isokinetic dynamometers and the technically limited handheld dynamometers. Therefore, the purpose of the present systematic review was to summarize the findings of the scientific literature related to the evaluation of eccentric strength of hamstring muscles with these new technologies. Methods: Systematic searches through the PubMed, Scopus, and Web of Science databases, from inception up to April 2020, were conducted for peer reviewed articles written in English, reporting eccentric strength of hamstrings assessed by devices, different to isokinetic and handheld dynamometers, in athletes. Results: Seventeen studies were finally included in the review with 4 different devices used and 18 parameters identified. The pooled sample consisted of 2893 participants (97% male and 3% female: 22 ± 4 years). The parameters most used were peak force (highest and average), peak torque (average and highest), and between-limb imbalance (left-to-right limb ratio). There is inconsistency regarding the association between eccentric hamstrings strength and both injury risk and athletic performance. There is no standardized definition or standardization of the calculation of the used parameters. Conclusions: The current evidence is insufficient to recommend a practical guide for sports professionals to use these new technologies in their daily routine, due to the need for standardized definitions and calculations. Furthermore, more studies with female athletes are warranted. Despite these limitations, the eccentric strength of hamstring muscles assessed by different devices may be recommended for monitoring the neuromuscular status of athletes

A Roadmap for HEP Software and Computing R&D for the 2020s

Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe

Particle packings and microstructure modeling of energetic materials

This dissertation explores the use of packings of frictionless hard particles as models of the microstructure of particulate heterogeneous materials. In the first part of this dissertation, we present the current mathematical framework used for understanding the properties of particle packings, as well as the methods and algorithms we have developed to generate packings of frictionless hard particles with a computer. We develop two algorithms to model hard-particle systems: a collision-driven molecular dynamics algorithm for the simulation of packings of spheres, and a novel hybrid algorithm employing both molecular dynamics and Monte Carlo techniques for the simulation of packings of particles with general convex shapes, such as spheres, cylinders, ellipsoids, polyhedra, etc. We focus heavily on performance in order to enable the simulation of large systems containing 10⁶–10⁷ particles, previously too computationally expensive to simulate. We use performance benchmarks to demonstrate that our implementations of these algorithms scale roughly linearly with the number N of particles in the system, and show the impact that polydispersivity has on performance. In the second part of this dissertation we explore the properties of disordered and ordered hard-particle packings. We reproduce key results found in the literature for packings of spheres and polyhedra, and discuss some of their statistical properties. We then follow the discussion with applications of particle packings as models of the microstructure of particulate materials obtained via computed tomography. We find that the shape of the particles and their size distribution both play a crucial role in the determination of the statistical properties of heterogeneous materials

Performance Analysis and Optimization on Linux

Lecture Contents In this lecture, we will look into the basics of CPU hardware architecture and how it relates to performance. We will also look into how to identify performance bottlenecks using a profiler, and what techniques can be used to mitigate different kinds of performance bottlenecks. Requirements Students should have basic familiarity with the Linux operating system, as well as with C and/or C++ programming languages. Knowledge about data structures and algorithms at a basic level is also good to have, but not strictly necessary. Short Speaker Bio Guilherme is a scientific software developer at CERN. He works on performance optimization of particle detector simulation software, as well as on porting simulation software to GPUs. Guilherme received his Ph.D. in aerospace engineering from the University of Illinois at Urbana-Chamapaign in 2014, and M.Sc. degree in physics from the University of Tokyo in 2007.</p

Gentoo Prefix as a Physics Software Manager

Gentoo Prefix is explored to manage sophisticated physics software stacks. It will be shown that Gentoo Prefix is an advantageous package management solution for big physics experiments, for its reusability on heterogeneous host environments, its vast collection of ebuild recipes, its extensibility for the future computing architectures and its deep root in an open diverse community inside and outside science