Configurable Strategies for Work-stealing

Work-stealing systems are typically oblivious to the nature of the tasks they are scheduling. For instance, they do not know or take into account how long a task will take to execute or how many subtasks it will spawn. Moreover, the actual task execution order is typically determined by the underlying task storage data structure, and cannot be changed. There are thus possibilities for optimizing task parallel executions by providing information on specific tasks and their preferred execution order to the scheduling system. We introduce scheduling strategies to enable applications to dynamically provide hints to the task-scheduling system on the nature of specific tasks. Scheduling strategies can be used to independently control both local task execution order as well as steal order. In contrast to conventional scheduling policies that are normally global in scope, strategies allow the scheduler to apply optimizations on individual tasks. This flexibility greatly improves composability as it allows the scheduler to apply different, specific scheduling choices for different parts of applications simultaneously. We present a number of benchmarks that highlight diverse, beneficial effects that can be achieved with scheduling strategies. Some benchmarks (branch-and-bound, single-source shortest path) show that prioritization of tasks can reduce the total amount of work compared to standard work-stealing execution order. For other benchmarks (triangle strip generation) qualitatively better results can be achieved in shorter time. Other optimizations, such as dynamic merging of tasks or stealing of half the work, instead of half the tasks, are also shown to improve performance. Composability is demonstrated by examples that combine different strategies, both within the same kernel (prefix sum) as well as when scheduling multiple kernels (prefix sum and unbalanced tree search)

Achieving a better balance between productivity and performance on FPGAs through Heterogeneous Extensible Multiprocessor Systems

Field Programmable Gate Arrays (FPGAs) were first introduced circa 1980, and they held the promise of delivering performance levels associated with customized circuits, but with productivity levels more closely associated with software development. Achieving both performance and productivity objectives has been a long standing challenge problem for the reconfigurable computing community and remains unsolved today. On one hand, Vendor supplied design flows have tended towards achieving the high levels of performance through gate level customization, but at the cost of very low productivity. On the other hand, FPGA densities are following Moore\u27s law and and can now support complete multiprocessor system architectures. Thus FPGAs can be turned into an architecture with programmable processors which brings productivity but sacrifices the peak performance advantages of custom circuits. In this thesis we explore how the two use cases can be combined to achieve the best from both. The flexibility of the FPGAs to host a heterogeneous multiprocessor system with different types of programmable processors and custom accelerators allows the software developers to design a platform that matches the unique performance needs of their application. However, currently no automated approaches are publicly available to create such heterogeneous architectures as well as the software support for these platforms. Creating base architectures, configuring multiple tool chains, and repetitive engineering design efforts can and should be automated. This thesis introduces Heterogeneous Extensible Multiprocessor System (HEMPS) template approach which allows an FPGA to be programmed with productivity levels close to those associated with parallel processing, and with performance levels close to those associated with customized circuits. The work in this thesis introduces an ArchGen script to automate the generation of HEMPS systems as well as a library of portable and self tuning polymorphic functions. These tools will abstract away the HW/SW co-design details and provide a transparent programming language to capture different levels of parallelisms, without sacrificing productivity or portability

Simulation of a flowing snow avalanche using molecular dynamics

This paper presents an approach for the modeling and simulation of a flowing snow avalanche, which is formed of dry and liquefied snow that slides down a slope, using molecular dynamics and the discrete element method. A particle system is utilized as a base method for the simulation and marching cubes with real-time shaders are employed for rendering. A uniform grid-based neighbor search algorithm is used for collision detection for interparticle and particleterrain interactions. A mass-spring model of the collision resolution is employed to mimic the compressibility of the snow and particle attraction forces are put into use between the particles and terrain surface. In order to achieve greater performance, general purpose GPU language and multithreaded programming are utilized for collision detection and resolution. The results are displayed with different combinations of rendering methods for the realistic representation of the flowing avalanche. © TÜB̄TAK

Gestion des réseaux multi-grappes hétérogènes avec la bibliothèque Madeleine III

This paper introduces the new version of the Madeleine portable multi-protocol communication library. Madeleine version III now includes full, flexible multi-cluster support associated to a redesigned version of the transparent multi-network message forwarding mechanism. Madeleine III works together with a new configuration management module to handle a wide panel of network-heterogeneous multi-cluster configurations. The integration of a new topology information system allows programmers of parallel computing applications to build highly optimized distributed algorithms on top of the transparent multi-network communication system provided by Madeleine III's virtual networks. The preliminary experiments we conducted regarding the new virtual network capabilities of Madeleine III showed interesting results with an asymptotic bandwidth of 43 MB/s over a virtual link made of a SISCI/SCI and a BIP/Myrinet physical link

How to Stop Under-Utilization and Love Multicores

Designing scalable transaction processing systems on modern hardware has been a challenge for almost a decade. Hardware trends oblige software to overcome three major challenges against systems scalability: (1) Exploiting the abundant thread-level parallelism provided by multicores, (2) Achieving predictively efficient execution despite the variability in communication latencies among cores on multisocket multicores, and (3) Taking advantage of the aggressive micro-architectural features. In this tutorial, we shed light on the above three challenges and survey recent proposals to alleviate them. First, we present a systematic way of eliminating scalability bottlenecks based on minimizing unbounded communication and show several techniques that apply the presented methodology to minimize bottlenecks in major components of transaction processing systems. Then, we analyze the problems that arise from the non-uniform nature of communication latencies on modern multisockets and ways to address them for systems that already scale well on multicores. Finally, we examine the sources of under-utilization within a modern processor and present insights and techniques to better exploit the micro-architectural resources of a processor by improving cache locality at the right level

Modernizing the core quantum chemistry algorithms

This document covers the basics of computational chemistry and how using the modern programming techniques the theory can be efficiently implemented on digital computers. The computer implementations are developed from the core two-electron integrals to many-body and coupled cluster algorithms. A particular attention is paid to the physical constraints of he computer resources and the emergence of the novel architectures

Doctor of Philosophy

dissertationStochastic methods, dense free-form mapping, atlas construction, and total variation are examples of advanced image processing techniques which are robust but computationally demanding. These algorithms often require a large amount of computational power as well as massive memory bandwidth. These requirements used to be ful lled only by supercomputers. The development of heterogeneous parallel subsystems and computation-specialized devices such as Graphic Processing Units (GPUs) has brought the requisite power to commodity hardware, opening up opportunities for scientists to experiment and evaluate the in uence of these techniques on their research and practical applications. However, harnessing the processing power from modern hardware is challenging. The di fferences between multicore parallel processing systems and conventional models are signi ficant, often requiring algorithms and data structures to be redesigned signi ficantly for efficiency. It also demands in-depth knowledge about modern hardware architectures to optimize these implementations, sometimes on a per-architecture basis. The goal of this dissertation is to introduce a solution for this problem based on a 3D image processing framework, using high performance APIs at the core level to utilize parallel processing power of the GPUs. The design of the framework facilitates an efficient application development process, which does not require scientists to have extensive knowledge about GPU systems, and encourages them to harness this power to solve their computationally challenging problems. To present the development of this framework, four main problems are described, and the solutions are discussed and evaluated: (1) essential components of a general 3D image processing library: data structures and algorithms, as well as how to implement these building blocks on the GPU architecture for optimal performance; (2) an implementation of unbiased atlas construction algorithms|an illustration of how to solve a highly complex and computationally expensive algorithm using this framework; (3) an extension of the framework to account for geometry descriptors to solve registration challenges with large scale shape changes and high intensity-contrast di fferences; and (4) an out-of-core streaming model, which enables developers to implement multi-image processing techniques on commodity hardware