Hierarchical Scheduling Framework Research Articles

Implementation of compositional scheduling framework on virtualization

Virtualization has been receiving increasing attention in embedded real-time systems. However, real-time systems, whose correctness depends on timing requirements, are not easily applicable to virtualization since virtualization mainly focuses on functional correctness. A hierarchical scheduling framework (HSF) provides a method of composing the complex timing requirements of real-time systems. There have been several works on the implementation of the HSF. Although the scheduling framework of virtualization directly corresponds to the HSF, they did not consider implementing the HSF on virtualization. In this paper, we implement a two-level HSF, where components use a periodic interface model using virtualization. We use an L4/Fiasco micro-kernel as a virtual machine monitor (VMM) and an L4Linux as a virtual machine (VM) and extend these to support real-time properties. The experimental results show that the HSF is suitable for the virtualization environment.

Overrun Methods and Resource Holding Times for Hierarchical Scheduling of Semi-Independent Real-Time Systems

The hierarchical scheduling framework (HSF) has been introduced as a design-time framework to enable compositional schedulability analysis of embedded software systems with real-time properties. In this paper, a software system consists of a number of semi-independent components called subsystems. Subsystems are developed independently and later integrated to form a system. To support this design process, in the paper, the proposed methods allow non-intrusive configuration and tuning of subsystem timing-behavior via subsystem interfaces for selecting scheduling parameters. This paper considers three methods to handle overruns due to resource sharing between subsystems in the HSF. For each one of these three overrun methods corresponding scheduling algorithms and associated schedulability analysis are presented together with analysis that shows under what circumstances one or the other is preferred. The analysis is generalized to allow for both fixed priority scheduling (FPS) and earliest deadline first (EDF) scheduling. Also, a further contribution of the paper is the technique of calculating resource-holding times within the framework under different scheduling algorithms; the resource holding times being an important parameter in the global schedulability analysis.

Hierarchical scheduling framework for QoS service in WiMAX point-to-multi-point networks

Quality of service (QoS) is an important issue in the deployment of broadband wireless access networks with real-time and non-real-time traffic integration. In this study, the authors propose a three-tier QoS service architecture and scheduling schemes to provide QoS supports in WiMAX networks with point-to-multi-point (PMP) topology. The distinct feature of the proposal is that QoS provisioning has been dynamically distributed to three tiers and implemented independently by both base station (BS) and subscriber stations (SSs). The performance of the proposed solution has been evaluated by extensive simulations and the theoretical analysis. The evaluation results show that our proposal can improve the performance of WiMAX PMP network much in terms of packet delay, packet loss rate and throughput.

A Hybrid Real-Time Scheduling Algorithm Based on Rigorously Proportional Dispatching of Serving

In hybrid real-time systems, schedulers must guarantee that all of hard real-time jobs are finished by their deadlines and the QoS of soft real-time tasks and non real-time tasks are improved as greatly as possible. This paper presents RPDS (rigorously proportional dispatching server) algorithm, and constructs a hierarchical scheduling framework based on that. RPDS partitions CPU time flow into continuous segments, and in each segment RPDS will forcibly assign one time slice to non-hard real-time tasks. Experimental results show that RPDS can allocate processor time to various application classes reasonably and reduce the deadline miss ratio of real-time

Earliest Deadline First Scheduling with Active Buffer Management for Real-Time Traffic in the Internet

We studied the problem of QoS guarantee for differentiated services. A two-level hierarchical scheduling framework was deployed to separate QoS metrics. Due to its desirable property of minimizing the maximum packet lateness, the Earliest Deadline First (EDF) scheduling was adopted to provide the in-class scheduling for the time-sensitive traffic. We employed an EDF scheduler combined with an active buffer management scheme (CHOKe) to improve the fairness of resource allocation and to maintain a good delay performance for real-time applications. Simulation results showed that the proposed scheme can achieve a better delay performance and make a more fair bandwidth allocation between the real-time TCP and UDP connections than the First Come First Served (FCFS) scheduling with the drop-tail buffer management which is commonly deployed in traditional IP routers.

Traffic scheduling in a photonic packet switching system with QoS guarantee

The main challenge in the design of future broadband networks is to efficiently support high-bandwidth multimedia services. Recent advances in the optical networking reveal that all optical networks offering multigigabit rate per wavelength may soon become economical as the underlying backbone in wide area networks, in which photonic switch plays a central role. Two issues are the essential in the design of photonic packet switching, the support of end-to-end virtual connections and the support of diverse quality-of-service (QoS) services. Existing work in wide-area optical networks has largely focused on the former, relatively less attention has been given to support heterogeneous traffic types and to satisfy the potentially different QoS requirements of different types of traffic. In this paper, we introduce a novel hierarchical scheduling framework to use in a class of photonic packet switching systems based on WDM, in which we separate the flow scheduling from the transmission scheduling. We show such separation is essential for achieving scalability such that large input-output ports can be accommodated, and also for offering flexibility in that optimal scheduling algorithms can be derived in different level that can be best tuned to the specific system requirements. The salient feature of the proposed scheduling mechanism is that it takes into account potentially different QoS requirements from different traffic flows. A number of interesting findings are observed from the results obtained by both analysis and simulation: (1) QoS requirements can be satisfied for both real-time and nonreal-time flows; (2) the impact Of the real-time traffic head-of-line (HoL) blocking on the system throughput can be effectively alleviated with the prevailing number of traffic flows. In addition, we investigate a variety of performance measures under different system configurations.

Aggregation and disaggregation of end items in a class of multistage production systems

Aggregation of end items in a class of multistage production systems within a hierarchical scheduling framework is considered. This class is one of flexible machining and assembly systems where each end item is assembled from a number of components. Each component undergoes a sequence of operations on various machines. The assembly structure of all items is flat. At least for some operations on some machines, set-ups are not negligible.