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 proliferation of communication-intensive real-time applications with "elastic" real-time constraints, such as streaming stored video, and the advent of differential services over the Internet require a new design for end-host communication subsystems. The design should (i) provide per-flow or per-service-class guarantees on the end-host, (ii) maximize the aggregate utility (or revenue) of the end-host's communication service across all clients, (iii) gracefully adapt to transient overload and resource shortage, and (iv) not starve lower-priority service classes during the period of sustained overload. This paper presents a new architecture for QoS-adaptive end-host communication subsystems in order to meet the above-stated goals. This architecture differs from others in that it provides generic end-host communication subsystem support for QoS-adaptive communication, as opposed to devising QoS adaptation for a particular type of real-time applications. Our architecture provides each...

Real-time systems are growing in complexity and realtime and soft real-time applications are becoming common in general-purpose computing environments. Thus, there is a growing need for scheduling solutions that simultaneously support processes with a variety of different timeliness constraints. Toward this goal we have developed the Resource Allocation/Dispatching (RAD) integrated scheduling model and the Rate-Based Earliest Deadline (RBED) integrated multi-class real-time scheduler based on this model. We present RAD and the RBED scheduler and formally prove the correctness of the operations that RBED employs. We then describe our implementation of RBED and present results demonstrating how RBED simultaneously and seamlessly supports hard real-time, soft real-time, and best-effort processes. 1.

When executing different real-time applications on a single processor system, one problem is how to compose these applications and guarantee at the same time that their timing requirements are not violated. A possible way of composing applications is through the resource reservation approach. Each application is handled by a dedicated server that is assigned a fraction of the processor. Using this approach, the system can be seen as a two-level hierarchical scheduler. A considerable amount of work has been recently addressed to the analysis of this kind of hierarchical systems. However, a question is still unanswered: given a set of real-time tasks to be handled by a server, how to assign the server parameters so that the task set is feasible? In this paper, we answer to the previous question for the case of fixed priority local scheduler by presenting a methodology for computing the class of server parameters that make the task set feasible.

When executing soft real-time tasks in a shared processor, it is important to properly allocate the computational resources such that the quality of service requirements of each task are satisfied. In this paper we propose Adaptive Reservations, based on applying a feedback scheme to a reservation based scheduler. After providing a precise mathematical model of the scheduler, we describe how this model can be used for synthesising the controller by applying results from control theory. Finally, we show the effectiveness of our method by simulation and by experiments with an MPEG player running on a modified Linux kernel. 1.

MS Manners is a mechanism that employs progress-based regulation to prevent resource contention with lowimportance processes from degrading the performance of high-importance processes. The mechanism assumes that resource contention that degrades the performance of a high-importance process will also retard the progress of the low-importance process. MS Manners detects this contention by monitoring the progress of the lowimportance process and inferring resource contention from a drop in the progress rate. This technique recognizes contention over any system resource, as long as the performance impact on contending processes is roughly symmetric. MS Manners employs statistical mechanisms to deal with stochastic progress measurements; it automatically calibrates a target progress rate, so no manual tuning is required; it supports multiple progress metrics from applications that perform several distinct tasks; and it orchestrates multiple low-importance processes to prevent measurement i...

In this paper, we argue that conventional operating systems need to be enhanced with predictable resource management mechanisms to meet the diverse performance requirements of emerging multimedia and web applications. We present QLinux---a multimedia operating system based on the Linux kernel that meets this requirement. QLinux employs hierarchical schedulers for fair, predictable allocation of processor, disk and network bandwidth, and accounting mechanisms for appropriate charging of resource usage. We experimentally evaluate the efficacy of these mechanisms using benchmarks and real-world applications. Our experimental results show that (i) emerging applications can indeed benefit from predictable allocation of resources, and (ii) the overheads imposed by the resource allocation mechanisms in QLinux are small. For instance, we show that the QLinux CPU scheduler can provide predictable performance guarantees to applications such as web servers and MPEG players, albeit at the expense of increasing the scheduling overhead from 1 s to 4 s. We conclude from our experiments that the benefits due to the resource management mechanisms in QLinux outweigh their increased overheads, making them a practical choice for conventional operating systems.

This paper introduces FARA, a framework that provides abstractions and mechanisms for building integrated adaptation and resource allocation services in complex real-time systems. FARA's design addresses (1) the specification of the adaptation capabilities of general-domain applications with multiple adaptive components and (2) the control of the adaptation impact on the satisfiability of an application's timing constraints during its transition to targeted steady state. We propose to use of a hierarchical adaptation model, to control the adaptation enactment overhead based on the costs of executing the application-specific adaptation procedures, and to reduce the decision overhead by use of effective solutions for mechanisms frequently invoked during the decision process, such as the decision context management and the allocation decision evaluation. 1. Introduction Complex real-time systems often rely on dynamic allocation of available resources in order to insure efficient and corre...

The popularity of mobile and networked applications has resulted in an increased demand for execution "sandboxes"---environments that impose irrevocable restrictions on resource usage. Existing approaches rely on kernel modification for enforcing quantitative restrictions (e.g., limiting CPU utilization of an application to 25%). However, the general applicability of such approaches is constrained by the difficulty of modifying shrink-wrapped operating systems such as Windows NT. This paper presents a user-level sandboxing approach for enforcing quantitative restrictions on resource usage of applications. Our approach actively monitors an application 's interactions with the underlying system, proactively controlling them to enforce the desired behavior. Our approach leverages a core set of user-level mechanisms that are available in most modern operating systems: fine-grained timers, monitoring infrastructure, debugger processes, priority-based scheduling, and pagebased memory protect...

Portable RK is a portable implementation of a resource kernel, a resource-centric approach to build a real-time kernel that provides explicit timely, guaranteed and enforced access by applications to system resources [13]. Portable RK is designed to work with widely available operating systems with minimal changes. This facilitates experimentation in a familiar software environment and helps the faster deployment of research results. Execution in resource kernels is directly based on OS-enforced resource reservation [7]. As a result, an application can request the reservation of a certain amount of a resource, and the kernel can guarantee that the requested amount is exclusively available to that application. In this paper, we describe the design and implementation of Portable RK called Linux/RK that resides within the Linux operating system. The evaluation results show that Portable RK in the form of Linux/RK gives direct control over timely resource utilization by applications and that its overhead costs are small enough to be negligible. 1