Real-time embedded systems can be found in a large number of devices we use, including safety-critical systems. Useful for their small size and low power consumption, they are also harder to protect against state-of-the-art attacks than general purpose systems due to their lack of hardware features. Even current defenses may not be applicable since instrumentation added to defend real-time embedded systems may cause them to miss their deadlines, rending them inoperable. We show that the static properties obtained by the scheduling policies can be used as security guarantees for the tasks composing the program. By completely securing a subset of the tasks of the program only using the scheduler policy, we remove the need to add external instrumentation on these tasks, reducing the amount of extra instructions needed to entirely protect the system. With less instrumentation, the overhead added by the defenses is reduced and can therefore be applied to a larger number of systems.

Esta dissertação tem por objetivo mostrar que se podem melhorar as capacidades de gerar, divulgar, documentar e processar informações que orientem os dirigentes de empresas de ônibus nas decisões sobre escalas de veículos. O processo usado para identificar e descrever relações entre escalas e operação de empresas de ônibus conteve entrevistas a executivos, administradores e funcionários. O processamento de dados se deu com o condicionamento de banco de dados e desenvolvimento de programa para computador. Para estudo de caso, adotaram-se dados coletados em uma empresa de transporte de passageiros por ônibus que opera em serviços urbanos, interurbanos, interestaduais, fretamento e turismo. / This dissertation has the objective to show that one can improve the capacities to generate, to publish, to document and to process information useful to guide the bus company\'s bosses on the decisions concerning the scales of vehicles. The process used to identify and to describe relationships between scales and operation of bus companies contained interviews to executives, administrators and employees. The data processing was done with the database conditioning and computer program development. For a case study, it was conducted a surveying in a passengers\' bus company that operates in services like urban, intercity, interstate, charter and tourism.

by Chi-lok Chan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1994. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Scheduling Problems of Chain-like Task System --- p.4 / Chapter 2.1 --- Introduction --- p.4 / Chapter 2.2 --- Problem Assumptions and Notations Definition --- p.7 / Chapter 2.3 --- Related Works --- p.9 / Chapter 2.3.1 --- Bokhari's Algorithm --- p.10 / Chapter 2.3.2 --- Sheu and Chiang's Algorithm --- p.12 / Chapter 2.3.3 --- Hsu's Algorithm --- p.12 / Chapter 2.4 --- Decision Algorithms for Un-mergeable Task System --- p.18 / Chapter 2.4.1 --- Feasible Length-K Schedule --- p.18 / Chapter 2.4.2 --- Generalized Decision Test --- p.23 / Chapter 2.5 --- Dominated and Non-dominated Task Systems --- p.26 / Chapter 2.5.1 --- Algorithm for Dominated Task System --- p.26 / Chapter 2.5.2 --- Property of Non-dominated Task System --- p.27 / Chapter 2.6 --- A Searching-Based Algorithm for the Optimization Problem --- p.28 / Chapter 2.6.1 --- Algorithm --- p.29 / Chapter 2.6.2 --- Complexity Analysis --- p.31 / Chapter 2.7 --- A Searching Algorithm Based on a Sorted Matrix --- p.33 / Chapter 2.7.1 --- Sorted Matrix --- p.33 / Chapter 2.7.2 --- Algorithm for the Optimization Problem --- p.35 / Chapter 2.7.3 --- Complexity Analysis --- p.40 / Chapter 2.8 --- A Constructive Algorithm for the Optimization Problem --- p.43 / Chapter 2.9 --- A Modified Constructive Algorithm --- p.46 / Chapter 2.9.1 --- Algorithm --- p.46 / Chapter 2.9.2 --- Worst-Case Analysis --- p.50 / Chapter 2.9.3 --- Sufficient Condition for Efficient Algorithm H --- p.58 / Chapter 2.9.4 --- Average-Case Analysis --- p.62 / Chapter 2.10 --- Performance Evaluation --- p.65 / Chapter 2.10.1 --- Optimal Schedule --- p.65 / Chapter 2.10.2 --- Space Complexity Analysis --- p.67 / Chapter 2.10.3 --- Time Complexity Analysis --- p.68 / Chapter 2.10.4 --- Simulation of Algorithm F and Algorithm H --- p.70 / Chapter 2.11 --- Conclusion --- p.74 / Chapter 3 --- Vehicle Scheduling Problems with Time Window Constraints --- p.77 / Chapter 3.1 --- Introduction --- p.77 / Chapter 3.2 --- Problem Formulation and Notations --- p.79 / Chapter 3.3 --- NP-hardness of VSP-WINDOW-SLP --- p.83 / Chapter 3.3.1 --- A Transformation from PARTITION --- p.83 / Chapter 3.3.2 --- Intuitive Idea of the Reduction --- p.85 / Chapter 3.3.3 --- NP-completeness Proof --- p.87 / Chapter 3.4 --- Polynomial Time Algorithm for the VSP-WINDOW on a Straight Line with Common Ready Time --- p.98 / Chapter 3.5 --- Strong NP-hardness of VSP-WINDOW-TREEP --- p.106 / Chapter 3.5.1 --- A Transformation from 3-PARTITION --- p.107 / Chapter 3.5.2 --- NP-completeness Proof --- p.107 / Chapter 3.6 --- Conclusion --- p.111 / Chapter 4 --- Conclusion --- p.115 / Bibliography --- p.119

by Hoi Wing, Yung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 56-60). / Abstracts in English and Chinese. / List of Figures --- p.v / List of Tables --- p.vi / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Literature Review --- p.3 / Chapter 1.2.1 --- On the Fixed Multiprocessor Job Scheduling Problems --- p.6 / Chapter 1.2.2 --- On the Nonfixed Multiprocessor Job Scheduling Problems --- p.8 / Chapter 1.3 --- Problem Formulation --- p.12 / Chapter 1.4 --- Organization of the Thesis --- p.13 / Chapter 2 --- Genetic Algorithms --- p.15 / Chapter 2.1 --- Basic Concepts --- p.15 / Chapter 2.2 --- Main components --- p.17 / Chapter 3 --- A New Genetic Algorithm --- p.24 / Chapter 3.1 --- Coding --- p.25 / Chapter 3.1.1 --- Simple Example --- p.28 / Chapter 3.2 --- Similarity of Chromosomes --- p.30 / Chapter 3.3 --- Fitness Evaluation --- p.33 / Chapter 3.4 --- Configurations --- p.35 / Chapter 3.4.1 --- Parent Selection --- p.35 / Chapter 3.4.2 --- Multipoint Crossover --- p.36 / Chapter 3.4.3 --- Multipoint Mutation --- p.38 / Chapter 3.4.4 --- Replacement Step --- p.38 / Chapter 3.4.5 --- Termination Criterion --- p.39 / Chapter 4 --- Experimental Results --- p.41 / Chapter 4.1 --- Total Weighted Completion Time --- p.41 / Chapter 4.1.1 --- Lee and Cai's Algorithm --- p.42 / Chapter 4.1.2 --- Computational Results --- p.44 / Chapter 4.1.3 --- On the Problem of Minimizing the Total Completion Time --- p.46 / Chapter 4.2 --- Makespan --- p.48 / Chapter 4.2.1 --- Mahesh's Algorithms and Linn & Chen's Algorithm --- p.48 / Chapter 4.2.2 --- Computational Results --- p.52 / Chapter 5 --- Conclusion --- p.54 / Bibliography --- p.56

Modern applications are increasingly backed by large-scale data centres. Systems software in these data centre environments, however, faces substantial challenges: the lack of uniform resource abstractions makes sharing and resource management inefficient, infrastructure software lacks end-to-end access control mechanisms, and work placement ignores the effects of hardware heterogeneity and workload interference. In this dissertation, I argue that uniform, clean-slate operating system (OS) abstractions designed to support distributed systems can make data centres more efficient and secure. I present a novel distributed operating system for data centres, focusing on two OS components: the abstractions for resource naming, management and protection, and the scheduling of work to compute resources. First, I introduce a reference model for a decentralised, distributed data centre OS, based on pervasive distributed objects and inspired by concepts in classic 1980s distributed OSes. Translucent abstractions free users from having to understand implementation details, but enable introspection for performance optimisation. Fine-grained access control is supported by combining storable, communicable identifier capabilities, and context-dependent, ephemeral handle capabilities. Finally, multi-phase I/O requests implement optimistically concurrent access to objects while supporting diverse application-level consistency policies. Second, I present the DIOS operating system, an implementation of my model as an extension to Linux. The DIOS system call API is centred around distributed objects, globally resolvable names, and translucent references that carry context-sensitive object meta-data. I illustrate how these concepts support distributed applications, and evaluate the performance of DIOS in microbenchmarks and a data-intensive MapReduce application. I find that it offers improved, finegrained isolation of resources, while permitting flexible sharing. Third, I present the Firmament cluster scheduler, which generalises prior work on scheduling via minimum-cost flow optimisation. Firmament can flexibly express many scheduling policies using pluggable cost models; it makes high-quality placement decisions based on fine-grained information about tasks and resources; and it scales the flow-based scheduling approach to very large clusters. In two case studies, I show that Firmament supports policies that reduce colocation interference between tasks and that it successfully exploits flexibility in the workload to improve the energy efficiency of a heterogeneous cluster. Moreover, my evaluation shows that Firmament scales the minimum-cost flow optimisation to clusters of tens of thousands of machines while still making sub-second placement decisions.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Alfred P. Sloan School of Management. / Vita. / Bibliography: leaves 187-191. / Ph.D.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Solving operations research problems with approximation algorithms has been an important topic since approximation algorithm can provide near-optimal solutions to NP-hard problems while achieving computational efficiency. In this thesis, we consider two different problems in the field of optimal control and scheduling theory respectively and develop efficient approximation algorithms for those problems with performance guarantee. Chapter 2 presents approximation algorithms for solving the optimal execution problem for demand-response contract in electricity markets. Demand side participation is essential for achieving real-time energy balance in today's electricity grid. Demand-response contracts, where an electric utility company buys options from consumers to reduce their load in the future, are an important tool to increase demand-side participation. In this chapter, we consider the operational problem of optimally exercising the available contracts over the planning horizon such that the total cost to satisfy the demand is minimized. In particular, we consider the objective of minimizing the sum of the expected ℓ_β-norm of the load deviations from given thresholds and the contract execution costs over the planning horizon. For β=∞, this reduces to minimizing the expected peak load. The peak load provides a good proxy to the total cost of the utility as spikes in electricity prices are observed only in peak load periods. We present a data driven near-optimal algorithm for the contract execution problem. Our algorithm is a sample average approximation (SAA) based dynamic program over a multi-period planning horizon. We provide a sample complexity bound on the number of demand samples required to compute a (1+ε)-approximate policy for any ε>0. Our SAA algorithm is quite general and we show that it can be adapted to quite general demand models including Markovian demands and objective functions. For the special case where the demand in each period is i.i.d., we show that a static solution is optimal for the dynamic problem. We also conduct a numerical study to compare the performance of our SAA based DP algorithm. Our numerical experiments show that we can achieve a (1+ε)-approximation in significantly smaller numbers of samples than what is implied by the theoretical bounds. Moreover, the structure of the approximate policy also shows that it can be well approximated by a simple affine function of the state. In Chapter 3, we study the NP-hard coflow scheduling problem and develop a polynomial-time approximation algorithm for the problem with constant approximation ratio. Communications in datacenter jobs (such as the shuffle operations in MapReduce applications) often involve many parallel flows, which may be processed simultaneously. This highly parallel structure presents new scheduling challenges in optimizing job-level performance objectives in data centers. Chowdhury and Stoica [13] introduced the coflow abstraction to capture these communication patterns, and recently Chowdhury et al. [15] developed effective heuristics to schedule coflows. In this chapter, we consider the problem of efficiently scheduling coflows so as to minimize the total weighted completion time, which has been shown to be strongly NP-hard [15]. Our main result is the first polynomial-time deterministic approximation algorithm for this problem, with an approximation ratio of $64/3$, and a randomized version of the algorithm, with a ratio of 8+16sqrt{2}/3. Our results use techniques from both combinatorial scheduling and matching theory, and rely on a clever grouping of coflows. In Chapter 4, we carry out a comprehensive experimental analysis on a Facebook trace and extensive simulated instances to evaluate the practical performance of several algorithms for coflow scheduling, including our approximation algorithms developed in Chapter 3. Our experiments suggest that simple algorithms provide effective approximations of the optimal, and that the performance of the approximation algorithm of Chapter 3 is relatively robust, near optimal, and always among the best compared with the other algorithms, in both the offline and online settings.

Com o aumento no uso de aglomerados e grades de computadores, cresce o interesse no estudo de comunicações entre processadores. Em um computador paralelo dedicado, ou em uma rede local homogênea, o tempo de comunicação é geralmente modelado de forma similar, independente de quais processadores estão se comunicando. Em uma rede onde os links entre os computadores são heterogêneos, computadores mais próximos tendem a apresentar menor latência e maior largura de banda do que computadores distantes. Além disso, a largura de banda agregada é diferente dependendo do número de conexões simultâneas existentes entre dois aglomerados distantes. Neste trabalho estudaremos a troca completa de mensagens de tamanhos diferentes entre aglomerados interligados por backbones. Proporemos um novo algoritmo de comunicação baseado em algoritmos conhecidos, apresentaremos simulações de escalonamentos dos algoritmos estudados para esta rede multi-aglomerado e analisaremos os resultados destas simulações. / The growth in popularity of clusters and computational grids caused an increase in the interest in studying interprocessors communications. The comunication time in a dedicated parallel computer or in a local homogeneous network is modeled in a similar way, regardless of which processors are communicating. In a network with heterogeneous links, closer computers generally have lower latency and larger bandwidth than wide area computers. Besides, the aggregated bandwidth depends on the number of simultaneous connections between two wide area clusters. In this work we study the complete exchange of messages of different sizes between interconnected clusters using a backbone. We propose a new comunication algorithm based on known algorithms, we present some scheduling simulations of the studied algorithms in this multi-cluster network and we present the results analysis of these simulations.