Analysis of tree-shaped transactions in distributed real time systems

A worst case response time analysis exploiting precedence constraints between fixed priority scheduled tasks in tree-shaped transactions is presented. The algorithm extends existing methods for analysis of linear transactions allowing a wider range of systems, in which tasks may trigger more than one succeeding task on their completion, i.e. the transactions form trees. It also improves existing methods, producing tighter response time bounds for tasks in both linear and tree-shaped transactions. The improvement is due to better exploitation of the precedence relations between tasks, which also makes the analysis faster than earlier. Simulation results show a significant reduction of estimated worst case response times when compared to earlier analysis methods for both linear and tree-shaped transactions. Such improvement leads to less pessimistic schedulability tests for distributed fixed priority scheduled systems.