Improved Schedulability Tests for Global Fixed-Priority Scheduling

In this paper, global fixed-priority multiprocessor scheduling of a set of sporadic real-time tasks is addressed. First, we propose a priority-assignment policy, called ISM-US, for implicit-deadline task systems. Policy ISM-US assigns slack monotonic priorities to a subset of the given task set and other tasks are assigned the highest fixed priority. We prove that the schedulability utilization bound for policy ISM-US is higher than the corresponding bound for any other existing schedulability test for implicit-deadline sporadic task systems. Second, we propose improvements to two state-of-the-art iterative schedulability tests for constrained-deadline sporadic task systems. Our improved schedulability tests, called HP-RTA-LC and HP-DA-LC, are based on a hybrid-priority assignment policy and are shown to dominate the two existing state-of-the-art tests, RTA-LC and DA-LC, respectively.