Analysis And Improvement Of Real-time Capability Of Embedded Linux2.6

Among main open source softwares,Linux is quickly entering the real-time controlfield with open kernel source codes,stable performance, UNIX compatibility,multiple processes applicability,great network capabilities,high security and pruned kernel. But as a general OS,its design rule is satisfying almost user ,not for embedded real-time application. Although 2.6 kernel has made much improvement than 2.4 kernel in supporting the real-time process with POSIX compliant real-time function,multithread,multitasks,preemptive kernel, O(1)scheduling algorithm,its real-time capability is very poor and can not ensure the response time of real-time task.This thesis mainly discusses the research and implement of Linux 2.6 hard performance in order to meet the needs in embedded field. It analyzes Linux2.6 kernel, especially process scheduler mechanism,interrupt mechanism,preemptive kernel, timer mechanism. On this basis,it put on three programs according to the shortage of poor real-time. Firstly, the threaded interrupt is picked out for heavy network load and I/O load in system.Secondly,As the improvement solution, The classical dynamic real-time scheduling algorithm—LLF(least laxity first) algorithm is introduced as to the problem of Linux 2.6 kernel lacking in real-time scheduling algorithms and policies in the scheduler mechanism, which enhances the system's real-time scheduler capability as well as maintains the original O(1)scheduling characteristic. Thirdly, as to the shortage of Linux 2.6 kernel's too large timer granularity in timer mechanism, One-shot Mode is introduced in Linux 2.6 timer from the principle of timer mechanism improvement in Kurt-Linux. The new timer mechanism is implemented skillfully for the combination of LLF algorithm and the one-shot mode. The new timer mechanism makes the system reached the microsecond level timer precision and maintains its original load capability.In the final part of the thesis , It tests the Linux 2.4 kernel, the Linux 2.6 kernel and the improved system on interrupt response time and context-switching time which are two key criterions of real-time testing .From the testing results, we can see that the improved Linux system has the stronger real-time capability than Linux 2.6 kernel. It is fitter for the high real-time application in embedded fields.