Notes

These policies are more complex to understand and implement than it seems! E.g.:

“I observed in the kernel code (to my disgust), the Linux PIP implementation is a nightmare: extremely heavy weight, involving maintenance of a full wait-for graph, and requiring updates for a range of events, including priority changes and interruptions of wait operations.“

“An additional reason is that the original specification of PIP [24], despite being informally “proved” correct, is actually flawed."

Quoted from ”Zhang, X., Urban, C. & Wu, C. Priority Inheritance Protocol Proved Correct. J Autom Reasoning 64, 73-95 (2020).

Equations in Buttazzo’s book

• In the equations for computing the blocking times, Buttazzo’s book has a ”-1“ factor affecting the critical region duration.

• This is due to the fact that he considers a clock resolution of 1 t.u.

• This means that if a t = tk a resource is busy then it was taken at least at t = tk − 1, so the task holding it already executed at least one time unit.

• In these slides I’m considering that the clock resolution is much smaller than the duration of tasks and critical sections, so that factor is neglected.

• Other than that the equations are similar.