Explicit Reservation of Local Memory in a Predictable, Preemptive Multitasking Real-Time System

Abstract

This paper proposes Carousel, a mechanism to manage local memory space, i.e. cache or scratch pad memory (SPM), such that inter-task interference is completely eliminated. The cost of saving and restoring the local memory state across context switches is explicitly handled by the preempting task, rather than being imposed implicitly on preempted tasks. Unlike earlier attempts to eliminate inter-task interference, Carousel allows each task to use as much local memory space as it requires, permitting the approach to scale to large numbers of tasks. Carousel is experimentally evaluated using a simulator. We demonstrate that preemption has no effect on task execution times, and that the Carousel technique compares well to the conventional approach to handling interference, where worst-case interference costs are simply added to the worst-case execution times (WCETs) of lower-priority tasks.