ABSTRACT
The scheduling analysis relies on a computing model with preemptible tasks. As soon as an event makes any task computable, the latter will contend for the processor, possibly becoming the current task in the case where its priority is greater than all the other computable tasks at that time. While in the model the task switch is considered instantaneous, in real-world systems this is not the case, and the delay between event occurrence and the consequent task switch may significantly alter the responsiveness of the system, possibly breaking its real-time requirements. This chapter discusses this issue with reference to the Linux operating system. It first discusses the aspects of the Linux kernel organization that adversely affect real-time responsiveness, and will then show how Linux evolved to overcome such effects. Afterwards, two nano-kernel based extension real-time of Linux, Xenomai and RTAI will be described to illustrate a different approach to achieving real-time responsiveness.
