The scheduling analysis introduced in previous chapters 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 will discuss this issue with reference to the Linux operating system.