Research And Design Of Scheduling Algorithm Based On RT-Linux

At present,it becomes more and more popular that different kinds of hard real-time and soft real-time task applications coexist in one system.The configurability and expansibility of real-time operating system are becoming increasingly important.Those real-time scheduling algorithms specially designed for hard real-time tasks are too single in application scope and can't to meet actual real-time needs entirely.Aiming at problem,this paper proposed a research target to improve scheduling performance and scheduling flexibility in embedded real-time operating system so as to support complex real-time application.This paper takes RT-Linux3.2 kernel as object for research.RT-Linux3.2 kernel scheduling strategy is a kind of preemptive static fixed priority scheduling.Before running of the system,it statically assigns a unique priority for each task.During the system running,the priority of a task is fixed.High-priority task will run first.Low-priority task can not run until the high-priority task abandons right to use CPU.Due to this scheduling mechanism,it will inevitably lead to a number of soft real-time tasks can't be timely responded in mix tasks set scheduling.This paper analyzes deficiency of the original algorithm,and on specific operation platforms,improves the scheduling algorithm part. EDF dynamic algorithm is embedded into the original algorithm firstly by modifying low layer data structure,adding of members variables associated with dynamic priority calculation and modifying function interfaces,so as to change original fixed priority scheduling core into a dynamic priority scheduling;Secondly,to properly response soft real-time tasks,a periodic server is added.The periodic server is set as a hard real-time task according to operating rules to compete CPU simultaneously with other hard real-time tasks.When periodic server gains the right to use CPU,soft real-time task is scheduled. Thus,on the basis of guaranteeing hard real-time tasks being completed before the deadline,missed deadline percentage of soft real-time tasks are also minimized,which makes up inadequacies in original algorithm. Finally,a testing scheme is designed to test and compare new algorithm and original one.By embedding hard real-time tasks and video software into the new kernel, correctness of EDF algorithm and operation status of soft real-time tasks under high load of the system are respectively verified.Test verification shows that hard real-time and soft real-time scheduling performance expected by the new algorithm is basically achieved. Other real-time performance can also meet needs of application.