Research And Realization Of Linux Real-time Scheduling Algorithm And Test Bench

The real-time system grows up very fast over the past several years, but the price of realtime operating system that can offer real-time functions is usually extremely expensive. Because of opening source code and excellent performance, Linux becomes new favourite in the real-time system field. But as a general timesharing operating system, Linux has a lot of shortcomings and deficiencies when it is used under the embedded and real-time environment, so the existing Linux should be transformed.Valuable research on the realization mechanism of each part of Linux operating system according to the characteristics of real-time system is described in this thesis, and several aspects unsuitble for real-time application have been improved.To operating system, Precise timing is very important for the correct scheduling and timely response of task. The grain size of periodic clock of Linux is 10ms, and too coarse for real-time systems. In order to increasing the precision of the clock in case of not losing performance , the scheme of scheduling real-time process is designed and realized with fine-grain clock interrupt produced by local APIC timer in the CPU of Intel PII series or above, and original Linux clock interrupt is not changed yet. In this way, the precision of the clock is increased, and performance is not lossed too, so problem of precision of the clock is well solved.Design of Linux operating system is used for time-sharing application, it's priority scheduling way does not relate with time, but each of real-time task have demand of deadline, three timers related with the time characteristic are used for change process's running state, then the process can be scheduled according to time's demand in the following scheduling function.The specific real-time scheduling algorithm is suitable for specific application. In order to examine the performance, general scheduling frame is adopted and realized in this thesis. This frame can use lots of real-time scheduling algorithm, time-driven algorithm is realized too.The experiment result proves that the improvement enables Linux to scheduling the realtime task of microsecond grade in the situation of not increasing system load.