Open Real-time Linux Research And Design

With the development of computer science and technology, the application field of real-time systems is continuously extended. And the scale and complexity of real-time systems are also increased continuously. Specially, lots of real-time systems will be related with network and multimedia applications in the network and multimedia development. So the cases that different kinds of hard real-time, soft real-time and non-real-time applications coexist in one system become more and more popular. This situation makes the real-time system become more complex and causes the inner framework of real-time system gains more and more attention from researchers.On the other hand, there are some new characteristics in these real-time systems. For example, the stream media usually needs the real-time system process some stream frames in some time. Moreover, the end system and the network must all provide QoS. In one hand, users and real-time systems can control the QoS status, in the other hand, the degrade QoS is also under control when the real-time system is unstable or overloads. Thus these soft real-time need a scheduling model, which can meet the demand of QoS and QoS can be integrated with scheduling. So we need a new scheduling model which is so flexible that we can quantificationally control the soft real-time system meet deadlines or not. In other words, the soft real-time system can guarantee that these deadlines are missed in right manner to hold the good behavior of real-time systems. Thus the real-time system can meet the demand of QoS.Based the realistic background, the thesis deeply researches the scheduling theory of the traditional open real-time system and proposes a new open real-time system —DWCS-ORTS(Dynamic Window-Constrained scheduling - Open Real-Time System). In an open real-time system, the undependent real-time applications can be designed independently and the schedulability can be tested online. Moreover, tasks can be loaded dynamically in an open real-time system. Dynamic Window-Constrained scheduling(DWCS) is a scheduling strategy based on the Window-Constrained model. It is a very flexiable scheduling algorithm and can be meet the demand of the above soft real-time systems.After this, the thesis proposes an adaptive QoS scheduling strategy, which uses the characteristics of DWCS. The design and scheme of the integrated scheduling framework are discussed with an actual operating system (Linux).DWCS-ORTS extends the traditional two-level scheduling scheme to two-level/three-level scheduling scheme based on the characteristics of real-time Linux. When the real-time system has not hard real-time tasks, it can use the two-level scheduling scheme. Otherwise, the real-time system need use the three-level scheduling scheme.DWCS-ORTS enables the concurrent running in the case that different kinds of real-time and non-real-time tasks coexist. The real-time tasks can be loaded dynamically without affecting other real-time tasks. The different kinds of real-time tasks can use different local schedulers and the local schedulers are uniformly scheduled by the operating system. In addition, DWCS holds out the QoS of the open real-time system very well and provides solving methods.For verifying the validity and actual efficiency of DWCS-ORTS, it must be im-...