Scalability in real-time systems with end-to-end requirements

The stringent demands to guarantee task deadlines in real-time systems have motivated both practitioners and researchers to look at ways to analyze systems prior to run-time. This paper reports a new perspective of analyzing real-time systems that in addition to ascertaining the ability of a system to meet task deadlines also qualifies these guarantees. The guarantees are qualified by a measure (called the scaling factor) of the system's ability to continue to provide these guarantees under possible changes to the tasks. This measure is shown to have many applications in the design (task execution time estimation), development (portability and fault tolerance) and maintenance (scalability) of real-time systems. The derivation of this measure in end-to-end systems requires that we solve two fundamental problems - the uni-processor schedulability problem and the uni-processor scalability problem. The uni-processor schedulability problem involves finding whether a set of tasks (with arbitrary non-zero arrival times) will meet its deadlines. The scalability problem seeks to find the maximum scaling factor with which the execution times of a set of tasks can be scaled without invalidating its schedulability, Optimal solutions to these two fundamental problems are presented.