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29th International Supercomputing Conference, ISC 2014

作者： Scogland, Thomas R. W. Feng, Wu-Chun Rountree, Barry De Supinski, Bronis R. Department of Computer Science Virginia Tech Blacksburg VA 24060 United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory Livermore CA 94551 United States

ISBN: (纸本)9783319075174

The popularity of heterogeneous computing continues to increase rapidly due to the high peak performance, favorable energy efficiency, and comparatively low cost of accelerators. However, heterogeneous programming models still lack the flexibility of their CPU-only counterparts. Accelerated OpenMP models, including OpenMP 4.0 and OpenACC, ease the migration of code from CPUs to GPUs but lack much of OpenMP's flexibility: OpenMP applications can run on any number of CPUs without extra user effort, but GPU implementations do not offer similar adaptive worksharing across GPUs in a node, nor do they employ a mix of CPUs and GPUs. To address these shortcomings, we present CoreTSAR, our library for scheduling cores via a task-size adapting runtime system by supporting worksharing of loop nests across arbitrary heterogeneous resources. Beyond scheduling the computational load across devices, CoreTSAR includes a memory-management system that operates based on task association, enabling the runtime to dynamically manage memory movement and task granularity. Our evaluation shows that CoreTSAR can provide nearly linear scaling to four GPUs and all cores in a node without modifying the code within the parallel region. Furthermore, CoreTSAR provides portable performance across a variety of system configurations. © Springer International Publishing Switzerland 2014.

关键词： Program processors

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Automatically adapting programs for mixed-precision floating-point computation 13

Automatically adapting programs for mixed-precision floating...

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27th ACM International Conference on Supercomputing, ICS 2013

作者： Lam, Michael O. Hollingsworth, Jeffrey K. De Supinski, Bronis R. Legendre, Matthew P. Dept. of Computer Science University of Maryland College Park MD United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory Livermore CA United States

ISBN: (纸本)9781450321303

As scientific computation continues to scale, efficient use of floating-point arithmetic processors is critical. Lower precision allows streaming architectures to perform more operations per second and can reduce memory bandwidth pressure on all architectures. However, using a precision that is too low for a given algorithm and data set leads to inaccurate results. In this paper, we present a framework that uses binary instrumentation and modification to build mixed-precision configurations of existing binaries that were originally developed to use only double-precision. This framework allows developers to explore mixed-precision configurations without modifying their source code, and it permits autotuning of floating-point precision. We include a simple search algorithm to automate identification of code regions that can use lower precision. Our results for several benchmarks show that our framework is effective and incurs low overhead (less than 10X in most cases). In addition, we demonstrate that our tool can replicate manual conversions and suggest further optimization;in one case, we achieve a speedup of 2X. © 2013 ACM.

关键词： Digital arithmetic

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Managing performance analysis with dynamic statistical projection pursuit

Managing performance analysis with dynamic statistical proje...

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1999 ACM/IEEE Conference on Supercomputing, SC 1999

作者： Vetter, Jeffrey S. Reed, Daniel A. Center for Applied Scientific Computing Lawrence Livermore National Laboratory LivermoreCA94550 United States Department of Computer Science University of Illinois UrbanaIL61801 United States

ISBN: (纸本)1581130910

computer systems and applications are growing more complex. Consequently, performance analysis has become more difficult due to the complex, transient interrelationships among runtime components. To diagnose these types of performance issues, developers must use detailed instrumentation to capture a large number of performance metrics. Unfortunately, this instrumentation may actually influence the performance analysis, leading the developer to an ambiguous conclusion. In this paper, we introduce a technique for focussing a performance analysis on interesting performance metrics. This technique, called dynamic statistical projection pursuit, identifies interesting performance metrics that the monitoring system should capture across some number of processors. By reducing the number of performance metrics, projection pursuit can limit the impact of instrumentation on the performance of the target system and can reduce the volume of performance data. © 1999 IEEE.

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Feature Identification and Extraction in Function Fields

Feature Identification and Extraction in Function Fields

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9th Joint Eurographics/IEEE VGTC Symposium on Visualization, EuroVis 2007

作者： Anderson, John C. Gosink, Luke J. Duchaineau, Mark A. Joy, Kenneth I. Institute for Data Analysis and Visualization Department of Computer Science University of California Davis United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory

ISBN: (纸本)9783905673456

We present interactive techniques for identifying and extracting features in function fields. Function fields map points in n-dimensional Euclidean space to 1-dimensional scalar functions. Visual feature identification is accomplished by interactively rendering scalar distance fields, constructed by applying a function-space distance metric over the function field. Combining visual exploration with feature extraction queries, formulated as a set of function-space constraints, facilitates quantitative analysis and annotation. Numerous application domains give rise to function fields. We present results for two-dimensional hyperspectral images, and a simulated time-varying, three-dimensional air quality dataset. © The Eurographics Association 2007.

关键词： Air quality

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Maximizing adaptivity in hierarchical topological models using cancellation trees

Maximizing adaptivity in hierarchical topological models usi...

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Workshop on Mathematical Foundations of scientific Visualization, computer Graphics, and Massive Data Exploration, 2004

作者： Bremer, Peer-Timo Pascucci, Valerio Hamann, Bernd Department of Computer Science University of Illinois Urbana-Champaign United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory United States Institute for Data Analysis and Visualization Department of Computer Science University of California Davis United States

ISBN: (纸本)9783642543005

We present a highly adaptive hierarchical representation of the topology of functions defined over two-manifold domains. Guided by the theory of Morse–Smale complexes, we encode dependencies between cancellations of critical points using two independent structures: a traditional mesh hierarchy to store connectivity information and a new structure called cancellation trees to encode the configuration of critical points. Cancellation trees provide a powerful method to increase adaptivity while using a simple, easy-to-implement data structure. The resulting hierarchy is significantly more flexible than the one previously reported (IEEE Trans. Vis. Comput. Graph. 10(4):385–396, 2004). In particular, the resulting hierarchy is guaranteed to be of logarithmic height. © 2009 Springer-Verlag Berlin Heidelberg.

关键词： Trees (mathematics)

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Adaptive energy-preserving algorithms for guiding center system

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Plasma science and Technology 2023年第4期25卷 11-22页

作者：朱贝贝刘健张嘉炜祝爱卿唐贻发 Department of Applied Mathematics School of Mathematics and PhysicsUniversity of Science and Technology BeijingBeijing 100083Peopleʼs Republic of China School of Nuclear Science and Technology University of Science and Technology of ChinaHefei 230026Peopleʼs Republic of China Advanced algorithm Joint Lab Shandong Computer Science CenterQilu University of TechnologyJinan 250014Peopleʼs Republic of China The State Key Laboratory of Scientific and Engineering Computing The Institute of Computational Mathematics and Scientific/Engineering ComputingAcademy of Mathematics and Systems ScienceChinese Academy of SciencesBeijing 100190Peopleʼs Republic of China School of Mathematical Sciences University of Chinese Academy of SciencesBeijing 100049Peopleʼs Republic of China

We develop two types of adaptive energy preserving algorithms based on the averaged vector field for the guiding center dynamics,which plays a key role in magnetized *** adaptive scheme is applied to the Gauss Legendre’s quadrature rules and time stepsize respectively to overcome the energy drift problem in traditional energy-preserving *** new adaptive algorithms are second order,and their algebraic order is carefully *** results show that the global energy errors are bounded to the machine precision over long time using these adaptive algorithms without massive extra computation cost.

关键词： guiding center system energy-preserving methods adaptive energy conservation

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A hybrid hardware/software approach to efficiently determine cache coherence bottlenecks 05

A hybrid hardware/software approach to efficiently determine...

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ICS05 - 19th ACM International Conference on Supercomputing

作者： Marathe, Jaydeep Mueller, Frank De Supinski, Bronis Department of Computer Science North Carolina State University Raleigh NC 27695-7534 Lawrence Livermore National Laboratory Center for Applied Scientific Computing L-561 Livermore CA 94551

ISBN: (纸本)9781595931672

High-end computing increasingly relies on shared-memory multiprocessors (SMPs), such as clusters of SMPs, nodes of chipmultiprocessors (CMP) or large-scale single-system image (SSI) SMPs. In such systems, performance is often affected by the sharing pattern of data within applications and its impact on cache coherence. Sharing patterns that result in frequent invalidations followed by subsequent coherence misses create cache coherence bottlenecks with significant performance penalties. Past work on identifying coherence bottlenecks based on tracing memory accesses incurs considerable runtime overhead and does not scale well with increasing problem sizes, which makes it infeasible to use with real-world programs. In this paper, we introduce a novel low-cost, hardware-assisted approach to determine coherence bottlenecks in shared-memory OpenMP applications. We assess the merits of our approach on a contemporary SMP platform. Specifically, we assess the feasibility of lossy tracing to pin-point coherence problems in applications. We evaluate the qualitative and quantitative trade-offs between tracing overhead and accuracy of the generated coherence traffic metrics, correlated to memory access points at the program source level. Our lossy tracing mechanism closely approximates the degree of accuracy of determining coherence misses in full traces for most of the benchmarks we study while reducing run-time execution overhead and trace sizes by one to two orders of magnitude. To the best of our knowledge, this novel method significantly outperforms any of the prior approaches and, for the first time, makes cache coherence analysis feasible for long-running applications. Copyright © 2005 ACM.

关键词： Buffer storage

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Quantifying the effectiveness of load balance algorithms 12

Quantifying the effectiveness of load balance algorithms

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26th ACM International Conference on Supercomputing, ICS'12

作者： Pearce, Olga Gamblin, Todd De Supinski, Bronis R. Schulz, Martin Amato, Nancy M. Department of Computer Science and Engineering Texas A and M University College Station TX United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory Livermore CA United States

ISBN: (纸本)9781450313162

Load balance is critical for performance in large parallel applications. An imbalance on today's fastest supercomputers can force hundreds of thousands of cores to idle, and on future exascale machines this cost will increase by over a factor of a thousand. Improving load balance requires a detailed understanding of the amount of computational load per process and an application's simulated domain, but no existing metrics sufficiently account for both factors. Current load balance mechanisms are often integrated into applications and make implicit assumptions about the load. Some strategies place the burden of providing accurate load information, including the decision on when to balance, on the application. Existing application-independent mechanisms simply measure the application load without any knowledge of application elements, which limits them to identifying imbalance without correcting it. Our novel load model couples abstract application information with scalable measurements to derive accurate and actionable load metrics. Using these metrics, we develop a cost model for correcting load imbalance. Our model enables comparisons of the effectiveness of load balancing algorithms in any specific imbalance scenario. Our model correctly selects the algorithm that achieves the lowest runtime in up to 96% of the cases, and can achieve a 19% gain over selecting a single balancing algorithm for all cases. Copyright 2012 ACM.

关键词： Supercomputers

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Improving the communication pattern in matrix-vector operations for large scale-free graphs by disaggregation

Improving the communication pattern in matrix-vector operati...

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作者： Kuhlemann, Verena Vassilevski, Panayot S. Department of Mathematics and Computer Science Emory University Atlanta GA 30322 United States Lawrence Livermore National Laboratory Center for Applied Scientific Computing Livermore CA 94551 United States

Matrix-vector multiplication is the key operation in any Krylov-subspace iteration method. We are interested in Krylov methods applied to problems associated with the graph Laplacian arising from large scale-free graphs. Computations with graphs of this type on parallel distributed-memory computers are challenging. This is due to the fact that scale-free graphs have a degree distribution that follows a power law, and currently available graph partitioners are not efficient for such an irregular degree distribution. The lack of a good partitioning leads to excessive interprocessor communication requirements during every matrix-vector product. We present an approach to alleviate this problem based on embedding the original irregular graph into a more regular one by disaggregating (splitting up) vertices in the original graph. The matrix-vector operations for the original graph are performed via a factored triple matrix-vector product involving the embedding graph. Even though the latter graph is larger, we are able to decrease the communication requirements considerably and improve the performance of the matrix-vector product. Copyright © by SIAM. Unauthorized reproduction of this article is prohibited.

关键词： Iterative methods

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Decoupled load balancing 2015

Decoupled load balancing

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20th ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming, PPoPP 2015

作者： Pearce, Olga Gamblin, Todd De Supinski, Bronis R. Schulz, Martin Amato, Nancy M. Department of Computer Science and Engineering Texas A and M University College StationTX United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory LivermoreCA United States

ISBN: (纸本)9781450332057

Modern scientific simulations divide work between parallel processors by decomposing a spatial domain of mesh cells, particles, or other elements. A balanced assignment of the computational load is critical for parallel performance. If the computation per element changes over the simulation time, simulations can use dynamic load balance algorithms to evenly redistribute work to processes. Graph partitioners are widely used and balance very effectively, but they do not strong scale well. Typical SPMD simulations wait while a load balance algorithm runs on all processors, so a poorly scaling algorithm can itself become a bottleneck. We observe that the load balance algorithm is separate from the main application computation and has its own scaling properties. We propose to decouple the load balance algorithm from the application, and to offload the load balance computation so that it runs concurrently with the application on a smaller number of processors. We demonstrate the costs of decoupling and offloading the load balancing algorithm from a Barnes-Hut application.

关键词： Dynamic loads

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