5807481
Compiler algorithms for event variable synchronization
Event variable synchronization is a well known mecha nism for enforcing data dependences in a program that runs in parallel on a shared memory multiprocessor This paper presents compiler algorithms to automati cally generate event variable synchronization code Pre viously published algorithms dealt with single parallel loops in which dependence distances are constant and known by the compiler However loops in real appli cation programs are often arbitrarily nested Moreover compilers are often unable to determine dependence dis tances In contrast our algorithms generate synchro nization code based directly on array subscripts and do not require constant distances in data dependences The algorithms are designed for arbitrarily nested loops in cluding triangular or trapezoidal loops
23434511
A Compiler-Assisted Scheme for Adaptive Cache Coherence Enforcement
15223856
Efficient collection of sensor data in remote fields using mobile collectors
This paper proposes using a mobile collector, such as an airplane or a vehicle, to collect sensor data from remote fields. We present three different schedules for the collector: round-robin, rate-based, and min movement. The data are not immediately transmitted to the base station after being sensed but buffered at a cluster head; hence, it is important to ensure the latency is within an acceptable range. We compare the latency and the energy expended of the three schedules. We use the ns-2 network simulator to study the scenarios and illustrate conditions under which rate-based outperforms round-robin in latency, and vice-versa. The benefit of min movement is in minimizing the energy expended
20563509
A theoretical foundation for program transformations to reduce cache thrashing due to true data sharing
Cache thrashing due to true data sharing can degrade the performance of parallel programs significantly. Our previous work showed that parallel task alignment via program transformations can be quite effective for the reduction of such cache thrashing. In this paper, we present a theoretical foundation for such program transformations. Based on linear algebra and the theory of numbers, our work analyzes the data dependences among the tasks created by a fork-join parallel program and determines at compile time how these tasks should be assigned to processors in order to reduce cache thrashing due to true data sharing. Our analysis and program transformations can be easily performed by compilers for parallel computers.
62173532
Efficient interprocedural analysis for program parallelization and restructuring
An approach to efficient interprocedural analysis for program parallelization and restructuring is presented. Such analysis is needed for parallelizing loops which contain procedure calls. Our approach captures call effect on data dependencies by propagating the precise information of array subscripts from the called procedure. This allows the optimizing compiler to choose an efficient yet precise data dependence test scheme depending on the complexity of array reference patterns. The other existing methods do not provide such flexibility, hence may suffer from either imprecision or inefficiency. The paper also discusses usage of classical summary information in several important transformations for program parallelization. Experimental results are reported.
6205132
Improving Data Locality by Array Contraction
Array contraction is a program transformation which reduces array size while preserving the correct output. In this paper, we present an aggressive array-contraction technique and study its impact on memory system performance. This technique, called controlled SFC, combines loop shifting and controlled loop fusion to maximize opportunities for array contraction within a given loop nesting. A controlled fusion scheme is used to prevent overfusing loops and to avoid excessive pressure on the cache and the registers. Reducing the array size increases data reuse because of the increased average number of memory operations on the same memory addresses. Furthermore, if the data size of a loop nest fits in the cache after array contraction, then repeated references to the same variable in the loop nest generate cache hits, assuming set conflicts are eliminated successfully.
856534
On achieving optimal throughput with network coding
With the constraints of network topologies and link capacities, achieving the optimal end-to-end throughput in data networks has been known as a fundamental but computationally hard problem. In this paper, we seek efficient solutions to the problem of achieving optimal throughput in data networks, with single or multiple unicast, multicast and broadcast sessions. Although previous approaches lead to solving NP-complete problems, we show the surprising result that, facilitated by the recent advances of network coding, computing the strategies to achieve the optimal end-to-end throughput can be performed in polynomial time. This result holds for one or more communication sessions, as well as in the overlay network model. Supported by empirical studies, we present the surprising observation that in most topologies, applying network coding may not improve the achievable optimal throughput; rather, it facilitates the design of significantly more efficient algorithms to achieve such optimality.
32094418
On Ranks of Matrices Associated with Trees
Abstract.A sign pattern matrix is a matrix whose entries are from the set {+,−,0}. The purpose of this paper is to obtain bounds on the minimum rank of any symmetric sign pattern matrix A whose graph is a tree T (possibly with loops). In the special case when A is nonnegative with positive diagonal and the graph of A is “star-like”, the exact value of the minimum rank of A is obtained. As a result, it is shown that the gap between the symmetric minimal and maximal ranks can be arbitrarily large for a symmetric tree sign pattern A.

2564683
Mining multimedia data
Data Mining is a young but flourishing field. Many algorithms and applications exist to mine different types of data and extract different types of knowledge. Mining multimedia data is, however, at an experimental stage.We have implemented a prototype for mining high-level multimedia information and knowledge from large multimedia databases. MultiMedia Miner has been designed based on our years of experience in the research and development of a relational data mining system, DBMiner, in the Intelligent Database Systems Research Laboratory, and a Content-Based Image Retrieval system from Digital Libraries, C-BIRD, in the Vision and Media Laboratory.MultiMediaMiner includes the construction of multimedia data cubes which facilitate multiple dimensional analysis of multimedia data, and the mining of multiple kinds of knowledge, including summarization, classification, and association, in image and video databases. The images and video clips used in our experiments are collected by crawling the WWW. Many challenges have yet to be overcome, such as the large number of dimensions, and the existence of multi-valued dimensions.
14889690
Performance-directed energy management for storage systems
Energy consumption has become an important issue in the design of battery-operated mobile devices and sophisticated data centers. The storage hierarchy, which includes memory and disks, is a major energy consumer in such systems; especially for high-end servers at data centers. Much work has focused on energy control algorithms for storage systems that transition a device into a low power mode when a certain usage function exceeds a specified threshold. These algorithms are difficult to use in real systems, however, because designers must painstakingly and manually tune threshold values, and even then a performance guarantee is difficult. To address these limitations, we develop three algorithms: 1) a performance guarantee technique that designers can use with any underlying energy-control algorithm 2) a performance-directed control algorithm that periodically assigns a static configuration to different devices by solving an optimization problem 3) another performance-directed control algorithm that dynamically self-tunes according to an optimal set of thresholds
11765097
IDGraphs: intrusion detection and analysis using histographs
Traffic anomalies and attacks are commonplace in today's networks and identifying them rapidly and accurately is critical for large network operators. For a statistical intrusion detection system (IDS), it is crucial to detect at the flow-level for accurate detection and mitigation. However, existing IDS systems offer only limited support for: 1) interactively examining detected intrusions and anomalies; 2) analyzing worm propagation patterns; 3) and discovering correlated attacks. These problems are becoming even more acute as the traffic on today's high-speed routers continues to grow. IDGraphs is an interactive visualization system for intrusion detection that addresses these challenges. The central visualization in the system is a flow-level trace plotted with time on the horizontal axis and aggregated number of unsuccessful connections on the vertical axis. We then summarize a stack of tens or hundreds of thousands of these traces using the histographs (Pin Ren and Watson, 2005) technique, which maps data frequency at each pixel to brightness. Users may then interactively query the summary view, performing analysis by highlighting subsets of the traces. For example, brushing a linked correlation matrix view highlights traces with similar patterns, revealing distributed attacks that are difficult to detect using standard statistical analysis. We apply IDGraphs system to a real network router data-set with 179M flow-level records representing a total traffic of 1.16TB. The system successfully detects and analyzes a variety of attacks and anomalies, including port scanning, worm outbreaks, stealthy TCP SYN floodings, and some distributed attacks.