Towards Exploiting the Preservation Strategy of Deferrable Servers

Worst-case response time analysis of hard real-time tasks under hierarchical fixed priority pre-emptive scheduling (H-FPPS) has been addressed in a number of papers. Based on an exact schedulability condition, we showed in [4] that the existing analysis can be improved for H-FPPS when de-ferrable servers are used. In this paper, we reconsider re-sponse time analysis and show that improvements are not straightforward, because the worst-case response time of a task is not necessarily assumed for the first job when re-leased at a critical instant. The paper includes a brief in-vestigation of best-case response times and response jitter. 1