Research And Design Of Real-time Scheduling Algorithm Supported For Hierarchical Hybird Scheduling Policy

With the increasingly widespread application of real-time systems, hard real-time tasks and soft real-time tasks coexist in the same system are becoming increasingly common. Although scheduling method for different types of real-time task proposed by emerging, how to schedule reasonable and effective to hybrid real-time systems tasks which have different time requirements, become a hot research issue. The objective is to design a hierarchical scheduling algorithm to try to improve the response speed of soft real-time and non-periodic tasks under the premise of periodic tasks in hard real-time to ensure the deadline.In this paper, RT-Linux3.2 core is the object of research. RT-Linux3.2 kernel is based on preemptive and static solid priority scheduling. According to comprehensive analysis of scheduling organizational structure and scheduling algorithm on real-time kernel, a layer hybrid scheduling algorithm based on proportional dispatching bandwidth server is implemented in RTLinux. The scheduling between task modules is based on time slice rotation, but the scheduling in task module is based on priority-based preemptive scheduling policy. Firstly, new algorithm add task module data structure in order to restore the control information of module which tasks belong to. Secondly, task scheduling parameters is modified just as add module identification which task belongs to in order to provide basis for the hierarchical scheduling of task module. Through modifying the interrupt time of scheduler and the interrupt processing of timer, it is to realize rotation scheduling between task modules. The function of select new task and preempt task is isolated from scheduler and independed package in order to modify the scheduler to adapt to different types of tasks. Through limiting the rules of switching between task modules, when a module occupy the resources, the tasks in the other module can't seize the resources and only the tasks in one module may preempt between each other.Through the reconstruction of the RTLinux kernel and the modifying of the scheduler, it implement the hierarchical scheduling, expand the categories of tasks and enhance the scheduler function. New kernel does not change the original priority preemptive scheduler and make it as the low level scheduler, at the same time it realizes rotation scheduling policy in which sub-module of different types dispatching time slice proportional.