In recent years, there has been a rapid and wide spread of nontraditional computing platforms, especially mobile and portable computing devices. As applications become increasingly sophisticated and processing power increases, the most serious limitation on these devices is the available battery life. Dynamic Voltage Scaling (DVS) has been a key technique in exploiting the hardware characteristics of processors to reduce energy dissipation by lowering the supply voltage and operating frequency. The DVS algorithms are shown to be able to make dramatic energy savings while providing the necessary peak computation power in general-purpose systems. However, for a large class of applications in embedded real-time systems like cellular phones and camcorders, the variable operating frequency interferes with their deadline guarantee mechanisms, and DVS in this context, despite its growing importance, is largely overlooked/under-developed. To provide real-time guarantees, DVS must consider deadlines and periodicity of real-time tasks, requiring integration with the real-time scheduler. In this paper, we present a class of novel algorithms called real-time DVS (RT-DVS) that modify the OS's real-time scheduler and task management service to provide significant energy savings while maintaining real-time deadline guarantees. We show through simulations and a working prototype implementation that these RT-DVS algorithms closely approach the theoretical lower bound on energy consumption, and can easily reduce energy consumption 20% to 40% in an embedded real-time system.

The paper presents exact schedulability analyses for real-time systems scheduled at run-time with a static priority pre-emptive dispatcher. The tasks to be scheduled are allowed to experience internal blocking (from other tasks with which they share resources) and (with certain restrictions) release jitter — such as waiting for a message to arrive. The analysis presented is more general than that previously published, and subsumes, for example, techniques based on the Rate Monotonic approach. In addition to presenting the theory, an existing avionics case study is described and analysed. The predictions that follow from this analysis are seen to be in close agreement with the behaviour exhibited during simulation studies. 1.

This paper argues for the need to design a new processor scheduling algorithm that can handle the mix of applications we see today. We present a scheduling algorithm which we have implemented in the Solaris UNIX operating system [Eykholt et al. 1992], and demonstrate its improved performance over existing schedulers in research and practice on real applications. In particular, we have quantitatively compared against the popular weighted fair queueing and UNIX SVR4 schedulers in supporting multimedia applications in a realistic workstation environment...

superclass for all monitor control policy objects. PRIORITYCEILINGEMULATION 87 6.1.1 Constructors public Monitor ontrt () 6.1.2 Methods public static void setMonitor Contr l(MonitorControl8 policy) Control the default monitor behavior for object monitors used by synchronized statements and methods in the system. The type of the policy object determines the type of behavior. Conforming implementations must support priority ceiling emulation and priority inheritance for fixed priority preemptive threads. Parameters: policy - The new monitor control policy. If null nothing happens. public static void setMonitor Contr l(java.lang.Object monitor MonitorControl 8 policy) Has the same effect as setMonitorControl(), except that the policy only affects the indicated object monitor. Parameters: monitor - The monitor for which the new policy will be in use. The policy will take effect on the first attempt to lock the monitor after the completion of this method. If null nothing wi...

Distributed real-time systems play a very important role in our modern society. They are used in aircraft control, communication systems, military command and control systems, factory automation, and robotics. However, satisfying the rigid timing requirements of various real-time activities in distributed real-time systems often requires ad hoc methods to tune the system's runtime behavior The objective of Real-Time Mach is to develop a real-time version of the Mach kernel which provides users with a predictable and reliable distributed real-time computing environment. In this paper

This paper presents a feedback control real-time scheduling (FCS) framework for adaptive real-time systems. An advantage of the FCS framework is its use of feedback control theory (rather than ad hoc solutions) as a scientific underpinning. We apply a control theory based methodology to systematically design FCS algorithms to satisfy the transient and steady state performance specifications of real-time systems. In particular, we establish dynamic models of real-time systems and develop performance analyses of FCS algorithms, which are major challenges and key steps for the design of control theory based adaptive real-time systems. We also present a FCS architecture that allows plug-ins of different real-time scheduling policies and QoS optimization algorithms. Based on our framework, we identify different categories of real-time applications where different FCS algorithms should be applied. Performance evaluation results demonstrate that our analytically tuned FCS algorithms provide robust transient and steady state performance guarantees for periodic and aperiodic tasks even when the task execution times vary by as much as 100% from the initial estimate.

This report extends the current analysis associated with static priority pre-emptive based scheduling to address the wider problem of analysing schedulability of a distributed hard real-time system; in particular it derives analysis for a distributed system where tasks with arbitrary deadlines communicate by message passing and shared data areas. A simple TDMA protocol is assumed, and analysis developed to bound not only the communications delays, but also the delays and overheads incurred when messages are processed by the protocol stack at the destination processor. The report illustrates how a windowbased analysis technique can be used to find the worst-case response times of a distributed task set. An extended example illustrating the application of the analysis is presented.

Multimedia applications have timing requirements that cannot generally be satisfied using the time-sharing scheduling algorithms of general purpose operating systems. Our approach is to provide the predictability of real-time systems while retaining the flexibility of a timesharing system. We designed a processor capacity reservation mechanism that isolates programs from the timing and execution characteristics of other programs in the same way that a memory protection system isolates them from outside memory accesses. In this paper, we describe a scheduling framework that supports reservation and admission control, and we introduce a novel reserve abstraction, specifically designed for the microkernel architecture, for measuring and controlling processor usage. We have implemented processor capacity reserves in Real-Time Mach, and we describe the performance of our system on several types of applications. 1

Power efficient design of real-time systems based on programmable processors becomes more important as system functionality is increasingly realized through software. This paper presents a powerefficient version of a widely used fixed priority scheduling method. The method yields a power reduction by exploiting slack times, both those inherent in the system schedule and those arising from variations of execution times. The proposed run-time mechanism is simple enough to be implemented in most kernels. Experimental results show that the proposed scheduling method obtains a significant power reduction across several kinds of applications.

We consider the problem of OS resource management for real-time and multimedia systems where multiple activities with different timing constraints must be scheduled concurrently. Time on a particular resource is shared among its users and must be globally managed in real-time and multimedia systems. A resource kernel is meant for use in such systems and is defined to be one which provides timely, guaranteed and protected access to system resources. The resource kernel allows applications to specify only their resource demands leaving the kernel to satisfy those demands using hidden resource management schemes. This separation of resource specification from resource management allows OS-subsystem-specific customization by extending, optimizing or even replacing resource management