Linux Real-time Multi-processor Technology Research,

With the improvement of hardware performance, RTOS needs better performance and more functions or services to meet the requirement of real-time application. The commercial RTOSs that exist today are either too simple in funtionality or too expensive in price. There is no such a RTOS that is open enough, standard, widely supported, efficient and cheap, So many institutes begin to research on turning the non-real-time universal operating systems into RTOS.Linux is naturally a good candidate, because it is capable of providing many services, supporting various hardware and modularized development. Besides, it is open-source and compatible with many international and industry standards. Due to its non-preemptive kernel, coarse time granularity, frequent disabled interrupt, virtual memory and other buffer mechanism, Linux is not so "real-time" as RTOS.There are two ways to improve the real-time performances of Linux. One way, Linux kernel can be modified directly to reduce the schedule latency and this is so-called soft real-time. The other way, the so called sub-kernel idea can be adopted, which adds an extra real-time kernel besides Linux kernel. The real-time kernel is in charge of managing and scheduling all the real-time tasks and Linux kernel is treated as a real-time kernel's task with the lowest priority.RTAI is a typical example of sub-kernel way. Theory and implementation of the RTAI are analysed and the deficiencies of RTAI are pointed out. Because of the shortage of schedule algorithms of RTAI in multi-processor systems, so a packet processor scheduling algorithm is proposed, which fully integrates the advantages of the local and global multi-processor scheduling algorithms. Packet processor scheduling algorithm makes up the shortage of local scheduling algorithm that the M highest priority tasks may not be schedulled firstly in the system that has M processors and overcome the problem of the big time consumption in globle scheduling algorithm. Two classic scheduling algorithms and packet processor scheduling algorithm are added to RTAI. RTAI tasks can be assigned to designated group, and every group can also choose their own scheduling algorithm. The simulation results show packet processor scheduling algorithm can improve effectively the real-time performance of RTAI in multi-processor systems, so RTAI's application area has been extended too.