Research On Window-Constrainted Real-Time System For QoS Based On Linux

The real-time system has characters such as response in time, high dependability, dedication and less artificial interference, it was used initially applied to the field of military and industrial control. However, with the rapid development of computer and internet technology, real-time technology has been applied more and more to soft real-time system (SRTS), such as real-time network transmission, video transmission and multimedia processing. This SRTS is different from hard real-time systems that mandatory limit the deadline of jobs, and different from some soft real-time systems that don't make exactly rules for jobs. These new applications have a certain quality of service (QoS) requirements, which need satisfy the deadlines and loss-tolerance for jobs. As a result of these new features, Traditional static real-time systems and common operation system that based on fair scheduling can't satisfy these new applications. At the same time, window theory of constraints have incomparable advantages than probability constraints in describing QoS, it receives the majority of scholars research andextensive attention in recent years.Based on the above background, this dissertation imports a QoS mechanism which described by window constraints into Linux kernel and uses a suitable scheduler for satisfying weakly hard real-time systems demands. And then contents about this were studied:1) Based on the research of window-constrained real-time system with (m,k) constraints, a non-overlapping assembled window-constrained real-time system with (m, k)(?) constraints is proposed. By the research on schedulability of this real-time system, a new assembled window-constrained scheduling (AWCS) algorithm is prompted. The AWCS takes full advantage of the peculiarity of assembled constraints, and allocates the priority considering the affection of this scheduling for the total window, which improves the schedulability and reduces the violations of assembled window constraints. The simulation shows the AWCS is better than general algorithms that allocate priority by comparing these constraints independently.2) Combining the advantages of assembled window-constraints in exactly describing Qos and designing scheduler. And for the bugs of standard Linux kernel only can supply three schedulers: SCHED_RR, SCHED_FIFOandSCHED_OTHER, which can't satisfy tasks' QoS. By using the method of lodable kernel model (LKM), this dissertation revised schedule()'s strategy, and give a concrete realization of the framework for AWCS in Linux kernel.