Open Real-time System Resources Shared Mixed Task Scheduling Strategy Research

The implementation of real-time systems is no more restricted to special fields like aerospace industry. Real-time systems has applied to multimedia systems, embedded systems etc. In these fields, most of tasks are Soft Real-Time task. Under this circumstance, use the traditional scheduling strategy to schedule SRT tasks means bad scheduling performance and serious waste of CPU resources. Hence, the Open Real-time Systems (also called Open Environment) was borne and became the focus of research.At present, the mainstream of scheduling strategies for Open Real-time Systems are based on RR(Resource Reservation), and researchers almost focus on CBS (Constant Bandwidth Server). However, CBS did not consider the circumstances that tasks could share the same resources. The scheduling strategies for open real-time systems where tasks can share resources through mutex semaphores can be divided into two kinds:static scheduling strategies which are based on SRP (Stack Resource Policy) and dynamic scheduling strategies which are similar to BWI, they can schedule tasks without any previous information.At first, this paper introduces the CBS. Three problems include Unused Bandwidth, Soft Resource Reservation and Constant Parameter which could influence the schedule performance of CBS will be analyzed, scheduling policy related to each problem will be introduced and their functional features and applying scope are pointed out.After that, Stack Resource Policy (SRP) and the strategies which based on SRP is introduced. Two problems of SRP are pointed out and the solutions are presented. After that, the Bandwidth Inheritance(BWI) and similar scheduling policies are introduced. This paper focuses on analyzeing the problem that under general circumstances, BWI can't guarantee the hard real-time task's deadline, and points out a solution called Resource Isolation Policy. Its basic rules and properties are presented. Based on RIP, paper introduces a hybrid scheduling strategy. It uses SRP and BWI respectively to schedule HRT task set and SRT task set. Compared with SRP, this strategy can maintain SRT task's dynamic property. Compared with BWI, this strategy can guarantee HRT tasks'schedulability and improve their scheduling performance. It suits for real operating systems but only needs to pay for the expense of some system resources.This Paper is going to introduce basic rules of this proposed hybrid scheduling strategy in detail. Properties and schedulable condition of this hybrid scheduling strategy are formally discussed. Examples are given.At last, a Real-time Simulation Tool called ORTSimu is constructed to schedule tasks under BWI and this proposed hybrid scheduling strategy. Validating that the experimental results satisfied the expectation through the timming diagram, system utilization and system error rate which produced by ORTSimu.