The Ceiling Adjustment Scheme for Improving the Concurrency ofReal - Time Systems with Mixed

When scheduling a mixed workload of hard and soft(or rm) deadline tasks, we should always guarantee the executions of hard deadline tasks. The priority inversion is one of the problems which may prevent such guarantee for hard deadline tasks. The Priority Ceiling Protocol(PCP) could be a solution to the priority inversion problem. However, the sigle blocking property of PCP is sometimes very restrictive. Such a restriction may increase the number of unnecessary blockings, resulting in the increase of response times and deadline misses of soft deadline tasks under overload situations. In this paper, we propose a new protocol called Ceiling Adjustment Scheme(CAS), which adjusts the ceilings of shared resources by using the slack blocking time of hard deadline tasks while meeting their deadlines. Our simulation study shows that CAS experiences signiicantly reduced number of blockings(priority inversions) compared to that of PCP, and hence it achieves faster response times and reduced miss rates of soft deadline tasks under overload situations.