Mixed Scheduling Strategy In Real-time Systems

The real-time scheduling ensures one of the characteristic important means of the real-time system, the domestic and international research in this respect is long-standing too. But, the multi-task scheduling problem in real-time system is relatively more complicated, the research of this subject is still very unripe, Especially the mixed task sets includes the sporadic tasks.According to the development request for the present real-time system, and a large number of periodic task, sporadic task and aperiodic task in practical application, I made a deep research to mixed scheduling policies of the real-time system in this paper.This paper has studied the key problem in the real-time system on the basis of existing theory:real-time scheduling algorithm and relevant content. The main content is as follows:1),By analyzing the characteristics of sporadic job, it is to release an sporadic job each time to scheduling sporadic jobs, scheduler accepts test to it. in the paper,it is on the basis of test based on slack computation, add to simple test, so can reduce the time complexity of the algorithm.2),According to the characteristic of the aperiodic jobs and a characteristic of the task sets in the paper, it has proposed DBS algorithm, This algorithm succeeded to the TBS algorithm bandwidth isolation,at the same time, having improved TBS algorithm, namely the size of the server is variable, so improve the utilization of CPU.3),Described integrate scheduling of periodic tasks, sporadic tasks and aperiodic tasks, have proposed a level scheme for integrated scheduling. The level scheme is through dividing the process of scheduling into two phases, the scheduler will be sieve and specific scheduling separate, so that a variety of scheduling policies are to support, compared to only one kind of scheduling policies to support the scheme, expanding the system can be used. And according to the Scheduling chart of level scheme, have analyzed and designed with Testing and screening server, EDF scheduling server, DBS scheduling server, system scheduling device. At the same time, it gives the schedulability analysis for this paper algorithm.4),On the basis of analyzing performance index of real-time system testing, have carried on the performance test from latency and switch over two respects to the level scheme, and has analyzed the test result.In the research field of the real-time system, especially in the systematic task scheduling direction, there are a lot already knowing and unknown academic problem not solved, for example, new method of the problem that solve systematic priority inversion, multiprocessor rate-monotonic algorithm can be convicted of scheduling problems, With the priority task of scheduling constraints, etc, At present, both the academic study of the hot spots.