Utilization bounds for schedulability of aperiodic tasks are new in real-time scheduling literature. All aperiodic bounds known to date apply only to independent tasks. They either assume a liquid task model (one with infinitely many infinitesimal tasks) or are limited to deadline-monotonic and earliest-deadline first scheduling. In this paper, the authors make two important contributions. First, they derive the first aperiodic utilization bound that considers a task model with resource requirements. Second, the new bound is a function of a parameter called preemptable deadline ratio that depends on the scheduling policy. We show that many scheduling policies can be classified by this parameter allowing per-policy bounds to be derived. Simulation results demonstrating the applicability of aperiodic utilization bounds are presented.

Statistical Rate Monotonic Scheduling (SRMS) is a generalization of the classical RMS results of Liu and Layland [LL73] for periodic tasks with highly variable execution times and statistical QoS requirements. The main tenet of SRMS is that the variability in task resource requirements could be smoothed through aggregation to yield guaranteed QoS. This aggregation is done over time for a given task and across multiple tasks for a given period of time. Similar to RMS, SRMS has two components: a feasibility test and a scheduling algorithm. SRMS feasibility test ensures that it is possible for a given periodic task set to share a given resource without violating any of the statistical QoS constraints imposed on each task in the set. The SRMS scheduling algorithm consists of two parts: a job admission controller and a scheduler. The SRMS scheduler is a simple, preemptive, fixed-priority scheduler. The SRMS job admission controller manages the QoS delivered to the various tasks through admi...

Load balancing is often used to ensure that nodes in a distributed systems are equally loaded. In this paper, we showthatfor real-time systems, load balancing is not desirable. In particular,

Real-time scheduling theory has developed powerful tools for translating conditions on aggregate system utilization into per-task schedulability guarantees. The main breakthrough has been Liu and Layland's utilization bound for schedulability of periodic tasks. In 2001 this bound was generalized by Abdelzaher and Lu to the aperiodic task case. In this paper, we further generalize the aperiodic bound to the case of multiprocessors, and present key new insights into schedulability analysis of aperiodic tasks.

In addition to correctness requirements, a real-time system must also meet its temporal constraints, often expressed as deadlines. We call safety or mission critical real-time systems which may miss some deadlines critical soft real-time systems to distinguish them from hard real-time systems, where all deadlines must be met, and from soft real-time systems which are not safety or mission critical. The performance of a critical soft real-time system is acceptable as long as the deadline miss rate is below an application specific threshold. Architectural features of computer systems, such as caches and branch prediction hardware, are designed to improve average performance. Deterministic real-time design and analysis approaches require that such features be disabled to increase predictability. Alternatively, allowances must be made for for their effects by designing for the worst case. Either approach leads to a decrease in average performance. Since critical soft real-time systems do not require that all deadlines be met, average performance can be improved by adopting a probabilitistic approach. In order to allow a trade-off between deadlines met and average

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In this paper, we present Slack Stealing Job Admission Control (SSJAC) -- a methodology for scheduling periodic firm-deadline tasks with variable resource requirements, subject to controllable Quality of Service (QoS) constraints. In a system that uses Rate Monotonic Scheduling, SSJAC augments the slack stealing algorithm of Thuel et al with an admission control policy to manage the variability in the resource requirements of the periodic tasks. This enables

In this paper, we derive a utilization bound on schedulability of apriodic tasks with arbitrary arrival times, execution times, and deadlines. To the author's knowledge, this is the first time a utilization bound is derived for the aperiodic task model. It allows constructing an O(1) admission test for aperiodic tasks. Earlier admission tests are at best O(n). We show that deadline-monotonic scheduling is the optimal fixed-priority scheduling policy for aperiodic tasks in the sense of maximizing the schedulable utilization bound. We prove that the optimal bound is 5=8. Our result is an extension of the well-known Liu and Layland's bound of ln 2 (derived for periodic tasks). The new bound is shown to be tight. We briefly generalize our results to tasks with multiple resource requirements and multiple processors. Dynamic priority scheduling (EDF) of aperiodic tasks is shown to have the same schedulability bound as for periodic tasks. Our findings are especially useful for an emerging ca...

In a wide variety of embedded control applications, it is often the energy resources that form the fundamental limits on the system, not the system's computing capacity. Various techniques have been developed to improve energy efficiency in hardware, such as Dynamic Voltage Scaling (DVS), effectively extending the battery life of these systems. However, a comprehensive mechanism of task adaptation is needed in order to make the best use of the available energy resources, even in the presence of DVS or other power-reducing mechanisms. Further complicating this are the strict timeliness guarantees required by real-time applications commonly found in embedded systems. This paper

Many mission-critical distributed real-time applications must handle aperiodic tasks with end-to-end deadlines. However, existing middleware (e.g., RT-CORBA) lacks schedulability analysis and run-time enforcement mechanisms needed to give online real-time guarantees for aperiodic tasks. The primary contribution of this work is the design, implementation, and performance evaluation of the first realization of deferrable server and admission control mechanisms for aperiodic tasks in middleware. Empirical results on a KURT-Linux testbed demonstrate the efficiency and effectiveness of our deferrable server and admission control mechanisms in TAO’s federated event service.