Constant-time admission control for Deadline Monotonic tasks

The admission control problem is concerned with determining whether a new task may be accepted by a system consisting of a set of running tasks, such that the already admitted and the new task are all schedulable. Clearly, admission control decisions are to be taken on-line, and hence, this constitutes a general problem that arises in many real-time and embedded systems. As a result, there has always been a strong interest in developing efficient admission control algorithms for various setups. In this paper, we propose a novel constant-time admission control test for the Deadline Monotonic (DM) policy, i.e., the time taken by the test does not depend on the number of admitted tasks currently in the system. While it is possible to adapt known utilization bounds from the literature to derive constant-time admission control tests (e.g., the Liu and Layland bound, or the more recent hyperbolic bound), the test we propose is less pessimistic. We illustrate this analytically where possible and through a set of detailed experiments. Apart from the practical relevance of the proposed test in the specific context of DM tasks, the underlying technique is general enough and can possibly be extended to other scheduling policies as well.