Improved schedulability analysis of implicit deadline tasks under limited preemption EDF scheduling

Limited-preemption forms of uniprocessor scheduling provide a practical trade-off between flexibility and system overheads in embedded kernels. This paper considers the limited-preemption scheduling of implicit deadline tasks using the EDF algorithm. Upper bounds for the occurrence of a deadline miss in these task sets are derived, and employed to create several sufficient schedulability tests of increasing complexity and tightness. Exact analysis is then considered, and an algorithm with polynomial-time complexity is developed for situations in which the CPU utilization is bounded to be less than unity. Experimentally, the sufficient tests are shown to have acceptance ratios increasing from ≈60% up to ≈ 99%, and the number of evaluated deadlines required for the exact test is reduced by several orders of magnitude over previously known techniques.