Shinpei Kato

Portioned EDF-based scheduling on multiprocessors

This paper presents an EDF-based algorithm, called Earliest Deadline Deferrable Portion (EDDP), for efficient scheduling of recurrent real-time tasks on multiprocessor systems. The design of EDDP is based on the portioned scheduling technique which classifies each task into a fixed task or a migratable task. A fixed task is scheduled on the dedicated processor without migrations. A migratable task is meanwhile permitted to migrate between the particular two processors. In order to curb the cost of task migrations, EDDP makes at most M -- 1 migratable tasks on M processors. The scheduling analysis derives the condition for a given task set to be schedulable. It is also proven that no tasks ever miss deadlines, if the system utilization does not exceed 65%. Beyond the theoretical analysis, the effectiveness of EDDP is evaluated through simulation studies. Simulation results show that EDDP achieves high system utilization with a small number of preemptions, compared with the traditional EDF-based algorithms.

Real-Time Scheduling with Task Splitting on Multiprocessors

This paper presents a real-time scheduling algorithm with high schedulability and few preemptions for multiprocessor systems. The algorithm is based on an unorthodox method called portioned scheduling that assigns each task to a particular processor like partitioned scheduling but can split a task into two processors if there is not enough capacity remaining on a processor. We describe an algorithm for assigning tasks to processors as well as an algorithm for scheduling the assigned tasks on per-processor. The schedulability analysis provides a formula to calculate the upper bound of the schedulable per-processor utilization for the algorithm. We then prove that the least upper bound of the whole system utilization is 50%. In addition, we propose heuristic procedures to improve schedulability. The simulation results show that the algorithm can often successfully schedule a task set with system utilization much higher than 50%, though the least upper bound is 50%. We also show that the algorithm achieves higher schedulability with fewer preemptions compared to the existing algorithms.

Semi-partitioned Fixed-Priority Scheduling on Multiprocessors

This paper presents a new algorithm for fixed-priority scheduling of sporadic task systems on multiprocessors.The algorithm is categorized to such a scheduling class that qualifies a few tasks to migrate across processors, while most tasks are fixed to particular processors. We design the algorithm so that a task is qualified to migrate, only if it cannot be assigned to any individual processors, in such a way that it is never returned to the same processor within the same period, once it is migrated from one processor to another processor. The scheduling policy is then conformed to Deadline Monotonic. According to the simulation results, the new algorithm significantly outperforms the traditional fixed-priority algorithms in terms of schedulability.

Work-Conserving Optimal Real-Time Scheduling on Multiprocessors

Extended T-N plane abstraction (E-TNPA) proposed in this paper realizes work-conserving and efficient optimal real-time scheduling on multiprocessors relative to the original T-N plane abstraction (TNPA). Additionally a scheduling algorithm named NVNLF (no virtual nodal laxity first) is presented for E-TNPA. E-TNPA and NVNLF relax the restrictions of TNPA and the traditional algorithm LNREF, respectively. Arbitrary tasks can be preferentially executed by both tie-breaking rules and time apportionment policies in accordance with various system requirements with several restrictions. Simulation results show that E-TNPA significantly reduces the number of task preemptions as compared to TNPA.

Portioned static-priority scheduling on multiprocessors

This paper proposes an efficient real-time scheduling algorithm for multiprocessor platforms. The algorithm is a derivative of the rate monotonic (RM) algorithm, with its basis on the portioned scheduling technique. The theoretical design of the algorithm is well implementable for practical use. The schedulability of the algorithm is also analyzed to guarantee the worst-case performance. The simulation results show that the algorithm achieves higher system utilizations, in which all tasks meet deadlines, with a small number of preemptions compared to traditional algorithms.

Energy-Efficient Optimal Real-Time Scheduling on Multiprocessors

Optimal real-time scheduling is effective to not only schedulability improvement but also energy efficiency for real-time systems. In this paper, we propose real-time static voltage and frequency scaling (RT-SVFS) techniques based on an optimal real-time scheduling algorithm for multiprocessors. The techniques are theoretically optimal when the voltage and frequency can be controlled both uniformly and independently among processors. Simulation results show that the independent RT-SVFS technique closely approaches the lower bound on energy consumption if the voltage and frequency can be controlled minutely.

Global EDF-Based Scheduling with Efficient Priority Promotion

This paper presents an algorithm, called Earliest Deadline Critical Laxity (EDCL), for the efficient scheduling of sporadic real-time tasks on multiprocessors systems. EDCL is a derivative of the Earliest Deadline Zero Laxity (EDZL) algorithm in that the priority of a job reaching certain laxity is imperiously promoted to the top, but it differs in that the occurrence of priority promotion is confined to at the release time or the completion time of a job. This modification enables EDCL to bound the number of scheduler invocations and to relax the implementation complexity of scheduler, while the schedulability is still competitive with EDZL. The schedulability test of EDCL is designed through theoretical analysis. In addition, an error in the traditional schedulability test of EDZL is corrected. Simulation studies demonstrate the effectiveness of EDCL in terms of guaranteed schedulability and exhaustive schedulability by comparing with traditional efficient scheduling algorithms.

Dynamic voltage and frequency scaling for optimal real-time scheduling on multiprocessors

Not only system performance but also energy efficiency is critically important for embedded systems. Optimal real-time scheduling is effective to not only schedulability improvement but also energy efficiency for the systems. In this paper, real-time dynamic voltage and frequency scaling (RT DVFS) techniques based on the theoretically optimal real-time static voltage and frequency scaling (RTSVFS) techniques proposed in our previous work are presented for multiprocessor systems. Simulation results show that RT-DVFS covers up the disadvantages of RT-SVFS in the sense that RTDVFS are not practically affected by the difference among systems, whereas the energy consumption of RT-SVFS highly depends on the selectable processor frequency especially in high system utilization.

Extended RT-Component Framework for RT-Middleware

Modular component-based robot systems require not only an infrastructure for component management, but also scalability as well as real-time properties. Robot Technology (RT)-Middleware is a software platform for such component-based robot systems. Each component in the RT-Middleware, so-called ``RT-Component supporting particular robot functions, is based on Common Object Request Broker Architecture (CORBA). Unfortunately, the RT-Middleware lacks the mechanism for real-time control. In this paper, we extend the framework of the RT-Components to take care of timing constraints. We first enable tasks to have different periods within each RT-Component. We then modify the packet format of the General Inter-ORB Protocol (GIOP) to transfer the information of timing constraints over RT-Components. The performance evaluation on ART-Linux shows that the extended RT-Component framework improves the schedulability of distributed real-time tasks, without causing critical overheads in unmarshaling the modified GIOP packets.

Scheduling Aperiodic Tasks Using Total Bandwidth Server on Multiprocessors

This paper presents real-time scheduling techniques for reducing the response time of aperiodic tasks scheduled with real-time periodic tasks on multiprocessor systems. Two problems are addressed in this paper: (i) the scheduling of aperiodic tasks that can be dispatched to any processors when they arrive, and (ii) the scheduling of aperiodic tasks that must be executed on particular processors on which they arrive. In order to improve the responsiveness to both types of aperiodic tasks, efficient dispatching and migration algorithms are designed based on the Earliest Deadline First (EDF) algorithm and the Total Bandwidth Server (TBS) algorithm. The effectiveness of the designed algorithms is evaluated through simulation studies.