Hierarchical Scheduling Mechanism Research Articles

Hierarchical Scheduling Mechanism Based on Relaxed Constraints for Complex Industrial Scenes

Hierarchical Scheduling Mechanism Based on Relaxed Constraints for Complex Industrial Scenes

Flow shop scheduling of hybrid make-to-stock and make-to-order in a distributed precast concrete production system

Prefabrication is not only economically optimal but also environmentally sustainable; hence, it is the future of construction. Furthermore, mass customization is the future of prefabrication. In the mass customization era, the production paradigm in precast concrete (PC) factories will inevitably shift toward a blend of make-to-order (MTO) and make-to-stock (MTS) from the current MTO dominant model. Because PC factories have more motivation to fulfill MTO orders to secure profit, a hierarchical scheduling mechanism of MTO first and MTS second seems reasonable. Meanwhile, an emerging trend of expanding factories overseas is observed in the PC industry, especially in land-scarce countries like Singapore. Given additional resources, the new multiple-factory production network leads to relatively relaxed MTO due dates, which makes the proposed hierarchical scheduling mechanism more sensible. However, finding an optimal production plan for hybrid MTO and MTS on multiple production lines is not easy. There is an assignment problem in addition to the scheduling problem. Both the assignment problem and the scheduling problem are in the class of combinatorial optimization problems (COPs). Given that the use of meta-heuristics for solving complex COPs is a rapidly growing research topic, this paper employs meta-heuristic methods to solve the two problems simultaneously. Comparisons between the genetic algorithm and the whale optimization algorithm are made. Through the computational evaluation of a test case, the performance and effectiveness of the proposed methods are verified.

Cooperative Token-Ring Scheduling For Input-Queued Switches

We present a novel distributed scheduling paradigm for Internet routers with input-queued (IQ) switches, called cooperative token-ring (CTR) that provides significant performance improvement over existing scheduling schemes with comparable complexity. Many classical schedulers for IQ switches employ round-robin arbiters, which can be viewed as non-cooperative token-rings, where a separate token is used to resolve contention for each shared resource (e.g., an output port) and each input port acquires a token oblivious of the state of other input ports. Although classical round-robin scheduling schemes achieve fairness and high throughput for uniform traffic, under non-uniform traffic the performance degrades significantly. We show that by using a simple cooperative mechanism between the otherwise non-cooperative arbiters, the performance can be significantly improved. The CTR scheduler dynamically adapts to non-uniform traffic patterns and achieves essentially 100% throughput. The proposed cooperative mechanism is conceptually simple and is supported by experimental results. To provide adequate support for rate guarantees in IQ switches, we present a weighted cooperative token-ring, a simple hierarchical scheduling mechanism. Finally, we analyze the hardware complexity introduced by the cooperative mechanism and describe an optimal hardware implementation for an N times N switch with time complexity of Theta(log N) and circuit size of Theta(N log N) per port.

The design and implementation of real-time schedulers in RED-linux

Researchers in the real-time system community have designed and studied many advanced scheduling algorithms. However, most of these algorithms have not been implemented since it is very difficult to support new scheduling algorithms on most operating systems. To address this problem, we enhance the scheduling mechanism in Linux to provide a flexible scheduling framework. In the real-time and embedded Linux (RED-Linux) project, we implement a general scheduling framework which divides the system scheduler into two components: dispatcher and allocator. The dispatcher provides the mechanism of system scheduling and resides in the kernel space. The allocator is used to define the scheduling policy and implemented as a user space function. This framework allows users to implement application-specific schedulers in the user space which is easy to program and to debug. The framework also relieves the deficiency from the stock Linux scheduler which is not designed for real-time applications. To further enhance its power, a hierarchical scheduling mechanism has been provided in RED-Linux to allow a system designer to integrate different real-time applications together. Using scheduling groups, real-time jobs can be managed and scheduled in a hierarchical manner. In this paper, we discuss how the group mechanism is implemented in RED-Linux.

Periodic and Aperiodic Task Scheduling in Strongly Partitioned Integrated Real-time Systems

To facilitate the integration of real-time applications in a common platform, temporal and spatial partitioning should be provided. A strongly partitioned integrated real-time system (SPIRIT) is reported in this paper that adopts a two-level hierarchical scheduling mechanism to ensure temporal partitioning. At the lower level, multiple partitions (applications) are dispatched under a cyclic scheduling, whereas, at the higher level, multiple periodic tasks of a partition are scheduled within the partition according to a fixed priority algorithm. The proposed Distance Constraint guaranteed Dynamic Cyclic (DC2( scheduler applies three basic operations, left-sliding, right-putting and compacting, to dynamically schedule aperiodic tasks and, in the meantime, guarantees the distance constraint characteristics of a partition cyclic schedule. In addition, the slack time calculation of these dynamic operations can be applied for scheduling hard aperiodic tasks. With simulation studies, we observe that the DC2 algorithm can result in a significant performance enhancement in terms of the average response time of soft aperiodic tasks and the acceptance rate for hard aperiodic tasks.