This paper generalizes the notion of utilization bounds for schedulability of aperiodic tasks to the case of distributed resource systems. In the basic model, aperiodically arriving tasks are processed by multiple stages of a resource pipeline within end-to-end deadlines. The authors consider a multi-dimensional space in which each dimension represents the instantaneous utilization of a single stage. A feasible region is derived in this space such that all tasks meet their deadlines as long as pipeline resource consumption remains within the feasible region. The feasible region is a multi-dimensional extension of the single-resource utilization bound giving rise to a bounding surface in the utilization space rather than a scalar bound. Extensions of the analysis are provided to non-independent tasks and arbitrary task graphs. We evaluate the performance of admission control using simulation, as well as demonstrate the applicability of these results to task schedulability analysis in the total ship computing environment envisioned by the US navy. Keywords: Real-time scheduling, schedulability analysis, utilization bounds, aperiodic tasks, total ship computing environment. 1

While utilization bound based schedulability test is simple and effective, it is often difficult to derive the bound itself. For its analytical complexity, utilization bound results are usually obtained on a case-by-case basis. In this paper, we develop a general framework that allows one to effectively derive schedulability bounds for a wide range of real-time systems with different workload patterns and schedulers. Our analytical model is capable of describing a wide range of tasks and schedulers ’ behaviors. We propose a new definition of utilization, called workload rate. While similar to utilization, workload rate enables flexible representation of different scheduling and workload scenarios and leads to uniform derivation of schedulability bounds. We derive a parameterized schedulability bound for static priority schedulers with arbitrary priority assignment. Existing utilization bounds for different priority assignments and task releasing patterns can be derived from our closed-form formula by simple assignments of proper parameters. 1.

Abstract. Unlike processing snapshot queries in a traditional DBMS, the processing of continuous queries in a data stream management system (DSMS) needs to satisfy quality requirements such as processing delay. When the system is overloaded, quality degrades significantly thus load shedding becomes necessary. Maintaining the quality of queries is a difficult problem because both the processing cost and data arrival rate are highly unpredictable. We propose a quality adaptation framework that adjusts the application behavior based on the current system status. We leverage techniques from the area of control theory in designing the quality adaptation framework. Our simulation results demonstrate the effectiveness of the control-based quality adaptation strategy. Comparing to solutions proposed in previous works, our approach achieves significantly better quality with less waste of resources. 1

Recurrent tasks.

Abstract. We propose FIT, a flexible, light-weight and real-time scheduling system for wireless sensor platforms. There are three salient features of FIT. First, its two-tier hierarchical framework supports customizable application-specific scheduling policies, hence FIT is very flexible. Second, FIT is light-weight in terms of minimizing thread number to reduce preemptions and memory consumption while at the same time ensuring system schedulability. We propose a novel Minimum Thread Scheduling Policy (MTSP) exploration algorithm within FIT to achieve this goal. Finally, FIT provides a detailed real-time schedulability analysis method to help check if application’s temporal requirements can be met. We implemented FIT on MICAz motes, and carried out extensive evaluations. Results demonstrate that FIT is indeed flexible and light-weight for implementing real-time applications, at the same time, the schedulability analysis provided can predict the real-time behavior. FIT is a promising scheduling system for implementing complex real-time applications in sensor networks. 1

Prior research on schedulability bounds focused primarily on bounding utilization as a means to meet deadline constraints. Non-trivial bounds were found for a handful of scheduling policies in which utilization is directly related to the ability of the policy to meet deadlines. Examples include Rate Monotonic, Deadline Monotonic and EDF scheduling. For most other scheduling policies, however, utilization is not correlated with schedulability. For example, shortest-job-first can miss deadlines at an arbitrarily low utilization. This raises the question of whether or not some other non-utilization-based metric might be more indicative of schedulability in those cases. This paper answers the above question positively by extending the notion of schedulability bounds, in a uniform manner, to arbitrary (fixed) priorities and non-utilization metrics. We present a simple function that generates the schedulability metric to be bounded from the definition of a fixed-priority scheduling policy, and derive a non-trivial schedulability bound on that metric for aperiodic tasks. It is shown that the generated metrics and bounds are valid in that no deadline misses occur when these bounds are not violated. This result allows efficient real-time admission control to be performed in systems with arbitrary fixed-priority scheduling policies. As an example, we illustrate applying schedulability bounds for admission control to shortest-jobfirst and velocity-monotonic scheduling. While the proposed non-utilization bounds and feasible regions are derived for fixed-priority scheduling policies, the authors are investigating extensions of the results to dynamic-priority scheduling.

Abstract—In real-time systems, utilization-based schedulability test is a common approach to determine whether or not tasks can be admitted without violating deadline requirements. The test is extremely simple, since it only needs to compare the utilization of the tasks with a predetermined bound. As such, utilization-based schedulability tests are suitable for online use. The challenge is how to derive a reasonable utilization bound for a given system. Most existing results are obtained on a case-by-case basis because of their analytical complexity. In this paper, we develop a flexible and unified representation framework of real-time systems (i.e., tasks and schedulers) based on network calculus techniques. Our representation framework, together with the proposed bound derivation method, leads to a general bound result, which is applicable to a large family of real-time systems. Index Terms—Workload rate, utilization, schedulability test, network calculus. Ç 1

Unlike snapshot queries in traditional databases, the processing of continuous queries in Data Stream Management Systems (DSMSs) needs to satisfy user-specified QoS requirements. In this paper, we focus on three major QoS parameters in a DSMS environment: processing delay, querying frequency and loss tolerance. To minimize processing delays, the Earliest Deadline First (EDF) CPU scheduling policy is recommended.

Blackouts in our daily life can be disastrous with enormous economic loss. Blackouts usually occur when appropriate corrective actions are not effectively taken for an initial contingency, resulting in a cascade failure. Therefore, it is critical to complete those tasks that are running power grid computing algorithms in the Energy Management System (EMS) in a timely manner to avoid blackouts. This problem can be formulated as guaranteeing end-to-end deadlines in a Distributed Real-time Embedded (DRE) system. However, existing work in power grid computing runs those tasks in an open-loop manner, which leads to poor guarantees on timeliness thus a high probability of blackouts. Furthermore, existing feedback scheduling algorithms in DRE systems cannot be directly adopted to handle with significantly different timescales of power grid computing tasks. In this paper, we propose a hierarchical control solution to guarantee the deadlines of those tasks in EMS by grouping them based on their characteristics. Our solution is based on well-established control theory for guaranteed control accuracy and system stability. Simulation results based on a realistic workload configuration demonstrate that our solution can guarantee timeliness for power grid computing and hence help to avoid blackouts. 1

Abstract — A major trend in a modern system-on-chip design is a growing system complexity, which results in a sharp increase of communication traffic on the on-chip communication bus architectures. In a real-time embedded system, task arrival rate, inter-task arrival time, and data size to be transferred are not uniform over time. This is due to the partial re-configuration of an embedded system to cope with dynamic workload. In this context, the traditional application specific bus architectures may fail to meet the real-time constraints. Thus, to incorporate the random behavior of on-chip communication, this work proposes an approach to synthesize an on-chip bus architecture, which is robust for a given distributions of random tasks. The randomness of communication tasks is characterized by three main parameters which are the average task arrival rate, the average inter-task arrival time, and the data size. For synthesis, an on-chip bus requirement is guided by the worst-case performance need, while the dynamic voltage scaling technique is used to save energy when the workload is low or timing slack is high. This, in turn, results in an effective utilization of communication resources under variable workload. I.