Contents 0.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 0.2 Modeling Mesh-based Computations as Graphs . . . . . . . . . . . . . . . . . . . . . . . . . . 3 0.3 Static Graph Partitioning Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 0.3.1 Geometric Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 0.3.2 Combinatorial Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 0.3.3 Spectral Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 0.3.4 Multilevel Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 0.3.5 Combined Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 0.3.6 Qualitative Comparison of Graph Partitioning Schemes . . . . . . . . . . . . . . . . . 16 0.4 Load Balancing of Adaptive Computations . . . . . .

. In many important computational mechanics applications, the computation adapts dynamically during the simulation. Examples include adaptive mesh refinement, particle simulations and transient dynamics calculations. When running these kinds of simulations on a parallel computer, the work must be assigned to processors in a dynamic fashion to keep the computational load balanced. A number of approaches have been proposed for this dynamic load balancing problem. This paper reviews the major classes of algorithms, and discusses their relative merits on problems from computational mechanics. Shortcomings in the state-of-the-art are identified and suggestions are made for future research directions. Key words. dynamic load balancing, parallel computer, adaptive mesh refinement 1. Introduction. The efficient use of a parallel computer requires two, often competing, objectives to be achieved. First, the processors must be kept busy doing useful work. And second, the amount of interprocess...

This paper describes basic programming technology to support irregular applications on scalable concurrent hardware and shows how the technology has been applied to a variety of large-scale industrial application problems. The technology is based on the concept of a concurrent graph library that provides an adaptive collection of light-weight threads that may relocate between computers dynamically. The graph is portable to a wide range of highperformance multicomputers, shared-memory multiprocessors, and networked workstations. For each machine it is optimized to take advantage of the best available underlying communication and synchronization mechanisms. The graph provides a framework for adaptive refinement of computations, automatic load balancing, and interactive, on-the-fly visualization. It has been applied to a variety of large scale irregular applications to provide portable, scalable implementations with substantial code reuse. The applications described in this article typify...

A dominant factor for the success of an Internet based Web service is the Quality of Service (QoS) perceived by its users. The principal QoS attributes these users perceive include those related to the service ÒresponsivenessÓ, i.e. the service availability and timeliness. In this paper, we argue that QoS can be provided by distributing the processing load among replicated Web servers, and that these servers can be geographically distributed across the Internet. In this context, we discuss strategies for load distribution, and summarize a number of alternative architectures that can implement those strategies. The principal figure of merit we use in order to assess the effectiveness of the load distribution strategies we discuss is the response time experienced by the users.

S. All local authors can be reached via e-mail at the address last-name@cs.unibo.it. Questions and comments should be addressed to tr-admin@cs.unibo.it. Recent titles from the UBLCS Technical Report Series 99-4 Comparing the QoS of Internet Audio Mechanisms via Formal Methods, A. Aldini, M. Bernardo, R. Gorrieri, M. Roccetti, March 1999. 99-5 Group-Enhanced Remote Method Invocations, A. Montresor, R. Davoli, O. Babaoglu, April 1999. 99-6 Managing Complex Documents Over the WWW: a Case Study for XML, P. Ciancarini, F. Vitali, C. Mascolo, April 1999. 99-7 Data-Flow Hard Real-Time Programs: Scheduling Processors and Communication Channels in a Distributed Environment, R. Davoli, F. Tamburini, April 1999. 99-8 The MPS Computer System Simulator, M. Morsiani, R. Davoli, April 1999. 99-9 Action Refinement, R. Gorrieri, A. Rensink, April 1999. 99-10 Proceedings of the Workshop on Virtual Documents, Hypertext Functionality and the Web, M. Milosavljevic, F. Vitali, C. Watters, May 1...

Since a static work distribution does not allow for satisfactory speed-ups of parallel irregular algorithms, there is a need for a dynamic distribution of work and data that can be adapted to the runtime behavior of the algorithm. Task pools are data structures which can distribute tasks dynamically to different processors where each task specifies computations to be performed and provides the data for these computations. This paper discusses the characteristics of taskbased algorithms and describes the implementation of selected types of task pools for shared-memory multiprocessors. Several task pools have been implemented in C with POSIX threads and in Java. The task pools differ in the data structures to store the tasks, the mechanism to achieve load balance, and the memory manager used to store the tasks. Runtime experiments have been performed on three different shared-memory systems using a synthetic algorithm, the hierarchical radiosity method, and a volume rendering algorithm.

We focus on mapping iterative algorithms onto heterogeneous clusters. The application data is partitioned over the processors, which are arranged along a virtual ring. At each iteration, independent calculations are carried out in parallel, and some communications take place between consecutive processors in the ring. The question is to determine how to slice the application data into chunks, and assign these chunks to the processors, so that the total execution time is minimized. A major

This dissertation presents techniques for fast rendering of parametric spline surfaces. It presents algorithms and data structures needed to support the thesis that real-time display of surfaces (represented parametrically) is indeed possible on current graphics systems that are optimized to display triangles. It analyzes the sources of bottleneck in surface rendering and derives techniques to display tens of thousands of B'ezier surfaces, 10 \Gamma 20 times a second, by efficiently utilizing the graphics hardware. In a more general framework, this work demonstrates the effectiveness of using higher-order surfaces, as opposed to polygons. Analytic representation of surfaces retains information that is often lost in a static translation to polygons. We meaningfully use this analytic information to obtain better images than those generated from purely polygonal models. On the other hand, since current graphics systems are optimized for displaying triangles, we perform on-line triangulati...

This paper presents techniques for dynamic load balancing in heterogeneous computing environments. That is, the techniques are designed for sets of machines with varying processing capabilities and memory capacities. These methods can also be applied to homogenous systems in which the effective compute speed or memory availability is reduced by the presence of other programs running outside the target computation. To handle heterogeneous systems, a precise distinction is made between an abstract quantity of work, which might be measured as the number of iterations of a loop or the count of some data structure, and the utilization of resources, measured in seconds of processor time or bytes of memory, required by that work. Once that distinction is clearly drawn, the modifications to existing load balancing techniques are fairly straight-forward. The effectiveness of the resulting load balancing system is demonstrated for a large-scale particle simulation on a network of heterogeneous P...

This paper describes a preliminary approach to the fusion of multi-spectral image data for the analysis of cervical cancer. The long-term goal of this research is to define spectral signatures and automatically detect cancer cell structures. The approach combines a multi-spectral microscope with an image analysis tool suite, MathWeb. The tool suite incorporates a concurrent Principal Component Transform (PCT) that is used to fuse the multi-spectral data. This paper describes the general approach and the concurrent PCT algorithm. The algorithm is evaluated from both the perspective of image quality and performance scalability. Keywords: concurrent computing, image fusion, principal component transform, spectral signature 1. GENERAL APPROACH This paper describes an approach to multi-spectral analysis of cervical cancer cells. The approach uses a multi-spectral microscope to capture pathology images at selected spectral wavelengths. The resulting multi-spectral image is directly manipu...