Real-Time Analysis of Servers for General Job Arrivals

Pratyush Kumar, Jian-Jia Chen, Lothar Thiele, Andreas Schranzhofer and Giorgio C. Buttazzo.
Proceedings of the 17th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2011), August 28th-31st, 2011. Toyama, Japan.
Several servers have been proposed to schedule streams of aperiodic jobs in the presence of other periodic tasks. Standard schedulability analysis has been extended to consider such servers. However, not much attention has been laid on computing the worst-case delay suffered by a given stream of jobs when scheduled via a server. Such analysis is essential for using servers to schedule hard real-time tasks. We illustrate, with examples, that well established resource models, such as supply bound function and models from Real-Time Calculus, do not tightly characterize servers. In this work, we analyze the server algorithm of the Constant Bandwidth Server and compute a provably tight resource model of the server. The approach used enables us to differentiate between the soft and hard variants of the server. A similar approach can be used to characterize other servers; the final results for which are presented.