Research Of Real Time Performance For Embedded Linux Operating System

The real-time operating system has been widely used in national defense, industrial automation, telecommunication and other embedded areas. Compared to the common operating system, the real-time operating system's main task is to conduct timely response. Any incident must be responded in strict and limit time when it occurred at random, even in a high load of the system, otherwise would cause serious consequences. Linux kernel 2.6 has been released at the end of 2003, which has been proved that it is a highly efficient and stable kernel. Compared with 2.4 kernel, although 2.6 has some new technology allows real-time performance has been greatly improved, such as preemptive kernel, new O(1) scheduling algorithm, there are still a large number of regions in the kernel where the regions can not be preemptive, which impact on the real-time performance of system. In addition, 2.6 kernel used the preemptive O(1) scheduler which is based on priority, but the preemptive priority must inevitably lead to the priority inversion problem which would cause task scheduling uncertain, which seriously impact on the real-time performance of system. Therefore, in order to meet the harsh requirements of embedded real-time operating system, the problem of real-time optimization of Linux 2.6 kernel has become an urgent need to solve.In this paper, based on the in-depth study of Linux kernel 2.6 and the real-time transformation thinking by Ingo Molnar, the Linux kernel 2.6 has been modified in direct way. Because Linux kernel 2.6 uses a large quantity of spinlock, leaving a large number of critical areas existing, they seriously affect real-time system. In order to skillfully achieve a new locking mechanism and improve the real-time performance of Linux 2.6, Mutex, a mutual demolition lock will be introduced to spinlock to make spinlock preemptive. The real-time problems caused by the interrupt of Linux kernel 2.6, will be solved by interrupt threaded approach. After interrupt threaded, interrupt as a kernel thread running will be given different real-time priority, the priority of real-time tasks can be higher than interrupt thread, so that real-time tasks can be as the implementation unit of the top priority to run, even there are still real-time guarantee in serious load. In order to ensure real-time system, this paper proposed the Priority Inheritance Protocol and the Priority Ceiling Protocol to solve the priority inversion problem caused by the O(1) scheduler of the Linux 2.6, and specifically analyzed of the implementation method of the Priority Inheritance Protocol in Linux 2.6 kernel.Finally, the system context switching time has been tested by LMbench software, the test results show that the real-time performance of the improved Linux kernel 2.6 has been further improved than the original Linux kernel 2.6 and the Linux kernel 2.4, and more applicable to the embedded real-time application.