The preemptive scheduling of systems of periodic tasks on a platform comprised of several identical multiprocessors is considered. A scheduling algorithm is proposed for static-priority scheduling of such systems; this algorithm is a simple extension of the uniprocessor ratemonotonic scheduling algorithm. It is proven that this algorithm successfully schedules any periodic task system with a worst-case utilization no more than a third the capacity of the multiprocessor platform; for the special case of harmonic periodic task systems, the algorithm is proven to successfully schedule any system with a worst-case utilization of no more than half the platform capacity.

Traditional multiprocessor real-time scheduling partitions a task set and applies uniprocessor scheduling on each processor. For architectures where the penalty of migration is low, such as uniform-memory access shared-memory multiprocessors, the non-partitioned method becomes a viable alternative. By allowing a task to resume on another processor than the task was preempted on, some task sets can be scheduled where the partitioned method fails. We address fixed-priority scheduling of periodically arriving tasks on Ñ equally powerful processors having a non-partitioned ready queue. We propose a new priorityassignment scheme for the non-partitioned method. Using an extensive simulation study, we show that the priorityassignment scheme has equivalent performance to the best existing partitioning algorithms, and outperforms existing fixed-priority assignment schemes for the non-partitioned method. We also propose a dispatcher for the nonpartitioned method which reduces the number of preemptions to levels below the best partitioning schemes.

This paper studies preemptive static-priority scheduling on multiprocessors. We consider two approaches: global pfair static-priority scheduling and partitioned traditional static-priority scheduling. We prove that if presented algorithms are used and if less than 50% of the capacity is used then all deadlines are met. It is known that no static-priority multiprocessor scheduling algorithm can achieve a utilization bound greater than 50%.

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

Multihop wireless sensor networks have recently emerged as an important embedded computing platform. This paper defines a quantitative notion of real-time capacity of a wireless network. Real-time capacity describes how much real-time data the network can transfer by their deadlines. A capacity bound is derived that can be used as a sufficient schedulability condition for a class of fixedpriority packet scheduling algorithms. Using this bound, a designer can perform capacity planning prior to network deployment to ensure satisfaction of applications ’ real-time requirements. 1

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A new feasibility test for preemptive scheduling of periodic or sporadic real-time tasks on a single-queue m-server system allows for arbitrary fixed task priorities and arbitrary deadlines. For the special case when deadline equals period and priorities are rate monotonic, any set of tasks with maximum individual task utilization umax is feasible if the total utilization does not exceed m(1 umax )/2 + umax .

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.

Improvements in schedulability tests for global fixed-priority and EDF scheduling in a homogeneous multiprocessor (symmetric multiprocessing) environment have shown that the worst-case guaranteed achievable utilization levels for global EDF scheduling equals what can be achieved with partitioned scheduling, and both ways of applying EDF scheduling out-perform fixed-priority scheduling, for sets of independent periodic or sporadic hard-deadline tasks with deadline equal to period. However, less is known about the comparative performance of the partitioned vs. global and EDF vs. fixed-priority approaches in the average and without the restriction that deadline equal period, and particular which of the known combinations of a scheduling algorithm and a sufficient a priori test of schedulability is more likely to succeed in verifiably scheduling a set of tasks to meet all deadlines. This paper compares the performance of several such combinations on a variety of pseudo-randomly chosen sets of sporadic tasks. 1

This survey covers hard real-time scheduling algorithms and schedulability analysis techniques for homogeneous multiprocessor systems. It reviews the key results in this field from its origins in the late 1960s to the latest research published in late 2009. The survey outlines fundamental results about multiprocessor real-time scheduling that hold independent of the scheduling algorithms employed. It provides a taxonomy of the different scheduling methods, and considers the various performance metrics that can be used for comparison purposes. A detailed review is provided covering partitioned, global, and hybrid scheduling algorithms, approaches to resource sharing, and the latest results from empirical investigations. The survey identifies open issues, key research challenges, and likely productive research directions.