Pessimistic Deadline Ceiling Protocol: a concurrency control protocol under earliest deadline first scheduling

Abstract

Priority inversion is one of the major sources which makes the real-time system unpredictable. The Stack Resource Policy (SRP) and the Dynamic Priority Ceiling Protocol (Dpcp) are two representative protocols that solve the priority inversion problem under earliest deadline first scheduling (EDF). Dpcp yields better performance but incurs more overhead than SRP. We propose a new algorithm called the Pessimistic Priority Ceiling Protocol (PDCP). PDCP is based on the notions of the inactive task and the pessimistic deadline, which are defined in the paper. PDCP uses the dynamic value for the priority to access a shared resource, and uses the static value for determining the resource ceiling. PDCP yields comparable performance with Dpcp yet incurs less overhead than Dpcp. When compared to SRP, PDCP yields better performance at a slightly higher overhead. In particular, PDCP has the same overhead as SRP if the depth of the resource nesting is 1.