Delayed Processing Technique in Critical Sections for Real-Time Linux

In a real-time Linux system, the critical sections are thought to be one of the main factors causing problems with the start of real-time tasks. Traditional approaches for overcoming this issue either provide less of a guarantee on the worst-case latency time of real-time tasks, or have heavy overhead on normal Linux tasks. In this paper, to guarantee the start time of a real-time task, the execution of a normal Linux task will be delayed, made to wait at the beginning of a critical section, on the assumption that the future execution of this section would lead to an unacceptable delay time in the start of the coming real-time task. In addition to this, to reduce the latency time of the real-time task, a technique is proposed in which hardware interrupts will not be prohibited in the most kernel´s critical sections, so the timer interrupt can enter the kernel with no or less delay time. Experimental results showed that the worst-case start latency of a real-time task is reduced to 16.7% of that in Linux 2.6.20, and the penalty to the normal tasks is light, in contrast to traditional approaches. The proposed technique is useful not only for constructing a real-time Linux, but also for developing other real-time systems in which the critical sections are significantly long.