This server keeps track of CPU reservations in DROPS. If a client wants to do a reservation, it asks the CPU reservation server to do so. Parameters of a reservation are the periority p, the period T, the WCET C and the optional deadline D. The server checks whether the reservations made so far will meet their deadlines given the new reservation would be admitted, and checks whether this holds for the new one. Therefore, the server performs a response-time analysis on the existing reservations with priorities less or equal to p. For the new reservation, reservations with priorities higher or equal are used for the analysis.
If no deadline is specified, the reservation is made, but no guarantees are given to the specified thread. That is, the thread may consume the given CPU time C without violating others reservations, but it is not shure that the thread will actually be scheduled within any time. This is the preferred mode for optional parts of the QaS scheduling, where an external admission scheme ensures a certain quality of service.
The CPU reservation server does not assign priorities. It is the responibility of the caller to use some external priority assignment scheme. The CPU reservation ensures that the threads having a reservation will indeed get the amount of CPU they requested before the dealine approaches.