Schedulability Analysis for Processors with Aging-Aware Autonomic Frequency Scaling

With the rapid progress in semiconductor technology and the shrinking of device geometries, the resulting processors are increasingly becoming prone to effects like aging and soft errors. As a processor ages, its electrical characteristics degrade, i.e., the switching times of its transistors increase. Hence, the processor cannot continue error-free operation at the same clock frequency and/or voltage for which it was originally designed. In order to mitigate such effects, recent research proposes to equip processors with special circuitry that automatically adapts its clock frequency in response to changes in its circuit-level timing properties (arising from changes in its electrical characteristics). From the point of view of tasks running on these processors, such autonomic frequency scaling(AFS) processors become slower as they gradually age. This leads to additional execution delay for tasks, which needs to be analyzed carefully, particularly in the context of hard real time or safety-critical systems. Hence, for real-time systems based on AFS processors, the associated schedulability analysis should be aging-aware which is a relatively unexplored topic so far. In this paper we propose a schedulability analysis framework that accounts such aging-induced degradation and changes in timing properties of the processor, when designing hard real-time systems. In particular, we address the schedulability and task mapping problem by taking a lifetime constraint of the system into account. In other words, the system should be designed to be fully operational (i.e., meet all deadlines) till a given minimum period of time (i.e., its lifetime). The proposed framework is based on an aging model of the processor which we discuss in detail. In addition to studying the effects of aging on the schedulability of real-time tasks, we also discuss its impact on task mapping and resource dimensioning.