Workstations and personal computers are increasingly being used for applications with real-time characteristics such as speech understanding and synthesis, media computations and I/O, and animation, often concurrently executed with traditional non-real-time workloads. This paper presents a system that can schedule multiple independent activities so that: . activities can obtain minimum guaranteed execution rates with application-specified reservation granularities via CPU Reservations, . CPU Reservations, which are of the form "reserve X units of time out of every Y units", provide not just an average case execution rate of X/Y over long periods of time, but the stronger guarantee that from any instant of time, by Y time units later, the activity will have executed for at least X time units, . applications can use Time Constraints to schedule tasks by deadlines, with on-time completion guaranteed for tasks with accepted constraints, and . both CPU Reservations and Time Constraints...

In this paper we propose changing the decades-old practice of allocating CPU to threads based on priority to a scheme based on proportion and period. Our scheme allocates to each thread a percentage of CPU cycles over a period of time, and uses a feedback-based adaptive scheduler to assign automatically both proportion and period. Applications with known requirements, such as isochronous software devices, can bypass the adaptive scheduler by specifying their desired proportion and/or period. As a result, our scheme provides reservations to applications that need them, and the benefits of proportion and period to those that do not. Adaptive scheduling using proportion and period has several distinct benefits over either fixed or adaptive priority based schemes: finer grain control of allocation, lower variance in the amount of cycles allocated to a thread, and avoidance of accidental priority inversion and starvation, including defense against denial-of-service attacks. This paper descr...

The exokernel operating system architecture safely gives untrusted software efficient control over hardware and software resources by separating management from protection. This paper describes an exokernel system that allows specialized applications to achieve high performance without sacrificing the performance of unmodified UNIX programs. It evaluates the exokernel architecture by measuring end-to-end application performance on Xok, an exokernel for Intel x86-based computers, and by comparing Xok’s performance to the performance of two widely-used 4.4BSD UNIX systems (Free-BSD and OpenBSD). The results show that common unmodified UNIX applications can enjoy the benefits of exokernels: applications either perform comparably on Xok/ExOS and the BSD UNIXes, or perform significantly better. In addition, the results show that customized applications can benefit substantially from control over their resources (e.g., a factor of eight for a Web server). This paper also describes insights about the exokernel approach gained through building three different exokernel systems, and presents novel approaches to resource multiplexing. 1

Hierarchical CPU scheduling has emerged as a way to (1) support applications with diverse scheduling requirements in open systems, and (2) provide load isolation between applications, users, and other resource principals. Most existing work on hierarchical scheduling has focused on systems that provide a fixed scheduling model: the schedulers in part or all of the hierarchy are specified in advance. In this paper we describe a system of guarantees that permits a general hierarchy of soft real-time schedulers—one that contains arbitrary scheduling algorithms at all points within the hierarchy—to be analyzed. This analysis results in deterministic guarantees for threads at the leaves of the hierarchy. We also describe the design, implementation, and performance evaluation of a system for supporting such a hierarchy in the Windows 2000 kernel. Finally, we show that complex scheduling behaviors can be created using small schedulers as components and describe the HLS programming environment. 1.

Language-based extensible systems such as Java use type safety to provide memory safety in a single address space. Memory safety alone, however, is not sufficient to protect different applications from each other. Such systems must support a process model that enables the control and management of computational resources. In particular, language-based extensible systems must support resource control mechanisms analogous to those in standard operating systems. They must support the separation of processes and limit their use of resources, but still support safe and efficient interprocess communication. We demonstrate how this challenge can be addressed in Java operating systems. First, we describe the technical issues that arise when implementing a process model in Java. In particular, we lay out the design choices for managing resources. Second, we describe the solutions that we are exploring in two complementary projects, Alta and GVM. GVM is similar to a traditional monolithic kernel, whereas Alta closely models the Fluke operating system. Features of our prototypes include flexible control of processor time using CPU inheritance scheduling, per-process memory controls, fair allocation of network bandwidth, and execution directly on hardware using the OSKit. Finally, we compare our prototypes with other language-based operating systems and explore the tradeoffs between the various designs. 1

In this thesis, we formalize the concept of an implicitly-controlled system, also referred to as an implicit system. In an implicit system, cooperating components do not explicitly contact other components for control or state information; instead, components infer remote state by observing naturally-occurring local events and their corresponding implicit information, i.e., information available outside of a defined interface. Many systems, particularly in distributed and networked environments, have leveraged implicit control to simplify the implementation of services with autonomous components. To concretely demonstrate the advantages of implicit control, we propose and implement implicit coscheduling, an algorithm for dynamically coordinating the time...

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As networks of workstations (NOW) emerge as a viable platform for a wide range of workloads, a new scheduling approach is needed to allocate the collection of resources across competing users. In this paper, we show that extensions to a proportional-share scheduler for improving response time can still fairly allocate resources to a mix of sequential, interactive, and parallel jobs in this distributed environment. We find that a proportional-share scheduler, specifically a stride-scheduler, running on each node in the cluster is a good building-block. Simple extensions are implemented and analyzed which provide better response-times for interactive jobs by giving those jobs their share of resources over a longer time-interval. When scheduling jobs across the cluster, we show that fairness can be guaranteed if each local scheduler knows the number of tickets issued to each user and if the tickets are balanced across all workstations. Finally, we show that a proportional-share of resourc...

Language-basedextensible systems, such as Java Virtual Machines and SPIN, use type safety to provide memory safety in a single address space. By using software to provide safety, they can support more efficient IPC. Memory safety alone, however, is not sufficient to protect different applications from each other. Such systems need to support a process model that enables the control and management of computational resources. In particular, language-based extensible systems should support resource control mechanisms analogous to those in standard operating systems. They need to support the separation of processes and limit their use of resources, but still support safe and efficient IPC. We demonstrate how this challenge is being addressed in several Java-based systems. First, we lay out the design choices when implementing a process model in Java. Second, we compare the solutions that have been explored in several projects: Alta, K0, and the J-Kernel. Alta closely models the Fluke oper...