Distributed Selfish Coaching

Although cooperation generally increases the amount of resources available to a community of nodes, thus improving individual and collective performance, it also allows for the appearance of potential mistreatment problems through the exposition of one node's resources to others. We study such concerns by considering a group of independent, rational, self-aware nodes that cooperate using on-line caching algorithms, where the exposed resource is the storage at each node. Motivated by content networking applications -- including web caching, CDNs, and P2P -- this paper extends our previous work on the on-line version of the problem, which was conducted under a game-theoretic framework, and limited to object replication. We identify and investigate two causes of mistreatment: (1) cache state interactions (due to the cooperative servicing of requests) and (2) the adoption of a common scheme for cache management policies. Using analytic models, numerical solutions of these models, as well as simulation experiments, we show that on-line cooperation schemes using caching are fairly robust to mistreatment caused by state interactions. To appear in a substantial manner, the interaction through the exchange of miss-streams has to be very intense, making it feasible for the mistreated nodes to detect and react to exploitation. This robustness ceases to exist when nodes fetch and store objects in response to remote requests, i.e., when they operate as Level-2 caches (or proxies) for other nodes. Regarding mistreatment due to a common scheme, we show that this can easily take place when the "outlier" characteristics of some of the nodes get overlooked. This finding underscores the importance of allowing cooperative caching nodes the flexibility of choosing from a diverse set of schemes to fit the peculiarities of individual nodes. To that end, we outline an emulation-based framework for the development of mistreatment-resilient distributed selfish caching schemes. Our framework utilizes a simple control-theoretic approach to dynamically parameterize the cache management scheme. We show performance evaluation results that quantify the benefits from instantiating such a framework, which could be substantial under skewed demand profiles.National Science Foundation (CNS Cybertrust 0524477, CNS NeTS 0520166, CNS ITR 0205294, EIA RI 0202067); EU IST (CASCADAS and E-NEXT); Marie Curie Outgoing International Fellowship of the EU (MOIF-CT-2005-007230

A study of sampling, granularity and localities in program restructuring

Program restructuring is a method to reduce the cost of program execution by improving the locality of the program\u27s reference behavior. Three aspects of program restructuring (sampling, granularity, localities) are studied in this research. The study of first aspect, sampling, shows that the high cost of a posteriori restructuring can be reduced considerably by a program restructuring method based on sampled reference strings rather than on complete reference string;The second aspect is granularity. Based on the studies of two different block sizes (the basic-block and the procedure block), it is found that the performance of restructuring using smaller blocks is not necessarily better;Finally, a new strategy-independent restructuring method, using both the critical and locality principles, is found to be more effective than any other existing restructuring methods;Results of measurements of paging performance obtained in the experiments are discussed. Both fixed-space and variable-space paging policies are considered

An accurate prefetching policy for object oriented systems

PhD ThesisIn the latest high-performance computers, there is a growing requirement for accurate prefetching(AP) methodologies for advanced object management schemes in virtual memory and migration systems. The major issue for achieving this goal is that of finding a simple way of accurately predicting the objects that will be referenced in the near future and to group them so as to allow them to be fetched same time. The basic notion of AP involves building a relationship for logically grouping related objects and prefetching them, rather than using their physical grouping and it relies on demand fetching such as is done in existing restructuring or grouping schemes. By this, AP tries to overcome some of the shortcomings posed by physical grouping methods. Prefetching also makes use of the properties of object oriented languages to build inter and intra object relationships as a means of logical grouping. This thesis describes how this relationship can be established at compile time and how it can be used for accurate object prefetching in virtual memory systems. In addition, AP performs control flow and data dependency analysis to reinforce the relationships and to find the dependencies of a program. The user program is decomposed into prefetching blocks which contain all the information needed for block prefetching such as long branches and function calls at major branch points. The proposed prefetching scheme is implemented by extending a C++ compiler and evaluated on a virtual memory simulator. The results show a significant reduction both in the number of page fault and memory pollution. In particular, AP can suppress many page faults that occur during transition phases which are unmanageable by other ways of fetching. AP can be applied to a local and distributed virtual memory system so as to reduce the fault rate by fetching groups of objects at the same time and consequently lessening operating system overheads.British Counci

Compiler-Driven Cache Policy (Known Reference String)

Increasing cache hit-ratios has proved to be instrumental in improving performance of cache-based computers. This is particularly true for computers which have a high cache-miss/cache-hit memory reference delay ratio. Although software policies are often used for main vs. secondary memory caching , the speed required for an implementation of a CPU vs. main memory cache policy has prompted only investigation of policies which can be implemented directly in hardware. Based on compile-time analysis, it is possible to predict program behavior, thereby increasing the hit-ratio beyond the capability of pure run-time (hardware) techniques. In this report, compiler-driven techniques for this kind of cache policy are described. The SCP Model (software cache policy model) provides an optimal cache prefetch and placement/replacement policy when given an arbitrary memory reference string. In addition to suggesting a simplified cache hardware model, the SCP Model can be applied to various cache organizations such as direct mapping, set associative, and full associative. Analytic results demonstrate significant improvements in cache performance. The current work discusses an optimal cache policy which applies where the string of references is known at compile time. However, this constraint can be relaxed to encompass reference strings which are known only statistically, i.e., reference strings in which data aliases make the target of some references ambiguous. Companion reports, currently in preparation, detail the extension of the SCP Model to incorporate aliases, code incorporating loops, and conditional branches

Optimal Capacitor Placement in Radial Distribution Systems using Artificial Bee Colony (ABC) Algorithm

This paper presents a new method which applies an artificial bee colony algorithm (ABC) for capacitor placement in distribution systems with an objective of improving the voltage profile and reduction of power loss. The solution methodology has two parts: in part one the loss sensitivity factors are used to select the candidate locations for the capacitor placement and in part two a new algorithm called Artificial Bee Colony Algorithm(ABC) is used to estimate the optimal size of capacitors at the optimal buses determined in part one. The ABC algorithm is a new population based meta heuristic approach inspired by intelligent foraging behavior of honeybee swarm. The advantage of ABC algorithm is that it does not require external parameters such as cross over rate and mutation rate as in case of genetic algorithm and differential evolution and it is hard to determine these parameters in prior. The other advantage is that the global search ability in the algorithm is implemented by introducing neighborhood source production mechanism which is a similar to mutation process. To demonstrate the validity of the proposed algorithm, computer simulations are carried out on 34-bus system and compared the results with the other approach available in the literature. The proposed method has outperformed the other methods in terms of the quality of solution and computational efficiency

Workshop on Verification and Theorem Proving for Continuous Systems (NetCA Workshop 2005)

Oxford, UK, 26 August 200