Schedulability Analysis of Hierarchical Real Time Systems under Shared Resources
Sharing resources in hierarchical real time systems implemented with reservation servers requires the adoption of special budget management protocols that preserve the bandwidth allocated to a specific component. In addition, blocking times must be accurately estimated to guarantee both the global feasibility of all the servers and the local schedulability of applications running on each component. This paper presents two new local schedulability tests to verify the schedulability of real time applications running on reservation servers under fixed priority and EDF local schedulers. Reservation servers are implemented with the BROE algorithm. A simple extension to the SRP protocol is also proposed to reduce the blocking time of the server when accessing global resources shared among components. The performance of the new schedulability tests are compared with other solutions proposed in the literature, showing the effectiveness of the proposed improvements. Finally, an implementation of the main protocols on a lightweight RTOS is described, highlighting the main practical issues that have been encountered.
IEEE Transactions on Computers