Section: New Results

Uniprocessor Real-Time Scheduling

Participants : Yves Sorel, Falou Ndoye, Daniel de Rauglaudre.

We proposed a new schedulability condition for dependent tasks executed on a uniprocessor which takes into account the exact preemption cost. Unlike the work presented in [10] which achieves that goal only for fixed priority tasks, our schedulability condition considers fixed as well as dynamic priorities tasks. Thus, we can overcome priority inversions involved by data dependent tasks. The schedulability analysis based on this schedulability condition led to an off-line scheduler [42] described by a scheduling table. Therefore, we have proposed an on-line time-trigger scheduler which implements this scheduling table. Compared to classical on-line schedulers, the proposed approach has two benefits. On the one hand the cost of the task selection amounts only to read the task to be executed in the scheduling table built off-line, rather than using on-line a scheduling algorithm like RM, DM, EDF, etc. On the other hand this cost is fixed since it does not depend on the number of ready tasks. In addition, with our on-line scheduler we do not need to synchronize, on-line, the utilization of the shared memory data, due to dependences, because this synchronization is performed during the off-line schedulability analysis.