Orientador: Paulo Lício de Geus / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-23T23:09:29Z (GMT). No. of bitstreams: 1 Pereira_AndreAugustodaSilva_M.pdf: 2078139 bytes, checksum: 3b321df6a81e4d3aaa8cf753b119f8a1 (MD5) Previous issue date: 2013 / Resumo: O resumo poderá ser visualizado no texto completo da tese digital / Abstract: The complete abstract is available with the full electronic document / Mestrado / Ciência da Computação / Mestre em Ciência da Computação

Magister Scientiae - MSc / Self-tuning has been an elusive goal for operating systems and is becoming a pressing issue for modern operating systems. Well-trained system administrators are able to tune an operating system to achieve better system performance for a specific system class. Unfortunately, the system class can change when the running applications change. The model for self-tuning operating system is based on a monitor-classify-adjust loop. The idea of this loop is to continuously monitor certain performance metrics, and whenever these change, the system determines the new system class and dynamically adjusts tuning parameters for this new class. This thesis described KernTune, a prototype tool that identifies the system class and improves system performance automatically. A key aspect of KernTune is the notion of Artificial Intelligence oriented performance tuning. Its uses a support vector machine to identify the system class, and tunes the operating system for that specific system class. This thesis presented design and implementation details for KernTune. It showed how KernTune identifies a system class and tunes the operating system for improved performance. / South Africa

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Hard real-time systems in robotics, space and military missions, and control devices are specified with stringent and critical time constraints. On the other hand, soft real-time applications arising from multimedia, telecommunications, Internet web services, and games are specified with more lenient constraints. Real-time systems can also be distinguished in terms of their implementation into preemptive and non-preemptive systems. In preemptive systems, tasks are often preempted by higher priority tasks. Non-preemptive systems are gaining interest for implementing soft-real applications on multithreaded platforms. In this dissertation, I propose a new algorithm that uses a two-level scheduling strategy for scheduling non-preemptive soft real-time tasks. Our goal is to improve the success ratios of the well-known earliest deadline first (EDF) approach when the load on the system is very high and to improve the overall performance in both underloaded and overloaded conditions. Our approach, known as group-EDF (gEDF), is based on dynamic grouping of tasks with deadlines that are very close to each other, and using a shortest job first (SJF) technique to schedule tasks within the group. I believe that grouping tasks dynamically with similar deadlines and utilizing secondary criteria, such as minimizing the total execution time can lead to new and more efficient real-time scheduling algorithms. I present results comparing gEDF with other real-time algorithms including, EDF, best-effort, and guarantee scheme, by using randomly generated tasks with varying execution times, release times, deadlines and tolerances to missing deadlines, under varying workloads. Furthermore, I implemented the gEDF algorithm in the Linux kernel and evaluated gEDF for scheduling real applications.

Purely functional languages--with static type systems and dynamic memory management using garbage collection--are a known tool for helping programmers to reduce the number of memory errors in programs. By using such languages, we can establish correctness properties relating to memory-safety through our choice of implementation language alone. Unfortunately, the language characteristics that make purely functional languages safe also make them more difficult to apply in a low-level domain like operating systems construction. The low-level features that support the kinds of hardware manipulations required by operating systems are not typically available in memory-safe languages with garbage collection. Those that are provided may have the ability to violate memory- and type-safety, destroying the guarantees that motivate using such languages in the first place. This work demonstrates that it is possible to bridge the gap between the requirements of operating system implementations and the features of purely functional languages without sacrificing type- and memory-safety. In particular, we show that this can be achieved by isolating the potentially unsafe memory operations required by operating systems in an abstraction layer that is well integrated with a purely functional language. The salient features of this abstraction layer are that the operations it exposes are memory-safe and yet sufficiently expressive to support the implementation of realistic operating systems. The abstraction layer enables systems programmers to perform all of the low-level tasks necessary in an OS implementation, such as manipulating an MMU and executing user-level programs, without compromising the static memory-safety guarantees of programming in a purely functional language. A specific contribution of this work is an analysis of memory-safety for the abstraction layer by formalizing a meaning for memory-safety in the presence of virtual-memory using a novel application of noninterference security policies. In addition, we evaluate the expressiveness of the abstraction layer by implementing the L4 microkernel API, which has a flexible set of virtual memory management operations.

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Thesis: B.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1980 / by Hong Kien Ong. / B.S. / B.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

Multitasking systems are becoming increasingly used for implementing real-time systems since they are well-suited to asynchronous, often overlapping, events. With the availability of kernels such as Hunter and Ready's VRTX Operating System components, multitasking becomes a good alternative to other implementations of real-time systems, such as interrupt-driven and polling systems. We developed a software design method and wrote a sample real-time system with many of the characteristics of typical real-time systems. This multitasking system uses a standard printer port to output bits which indicate the various activities of the tasks in the system. It also allows the user to interactively change the priorities of the tasks and to modify parameters which determine how long and how often the tasks execute. Through the use of the printer port connected to a logic analyzer and the ability to change various parameters in the system dynamically, the interaction between tasks was studied for different situations. The observed interaction between tasks was consistent with intuition. We observed task pre-emption, tasks waiting for results from other tasks and the system overhead required for context switching. When the timing restrictions were increased, we observed that data is lost during intertask communication and that higher priority tasks are the only tasks which run. This ability to observe the interaction between tasks has removed much of the mystery surrounding multitasking. / M.S.

Resource Management is an extremely important concern for the network manager. Of the bus, ring and the star network topologies, usually employed in a local area network, the bus topology provides the highest reliability. However, peer-to-peer protocols usually followed in such a topology, make it extremely difficult to incorporate resource management features at a lower level of network architecture. This thesis presents design considerations for a session-level network controller, to be implemented on a local area network with a bus topology. The controller, will provide essential resource management, and attempt to improve the throughput of the network. The design is based on a single-board computer, and a streamlined operating system is also included in the design. It is claimed that such an environment will be ideal for networking tasks, like the controller presented. The design is software-oriented, though device selection is discussed, both for the controller and its network interface. The local area network used for the development of this project is a sixteen hundred node campus network at Virginia Tech ( using LocalNet 20) supplied by SYTEK, Inc. / M.S.

No description available.