Rapid and low-cost context-switch through embedded processor customization for real-time and control applications

In this paper, we present a methodology for low-cost and rapid context switch for multithreaded embedded processors with realtime guarantees. Context-switch, which involves saving and restoring the thread state, has constituted not only a large performance overhead for many multithreaded embedded systems, but also an obstacle creating a significant delay in the response time for many time-critical control applications. The proposed technique exploits application information extracted during compile time to make sure that only a minimal amount of thread state is saved and subsequently restored on preemption. The register liveness within the application inner loops is analyzed and a few points, referred to as switch points, are identified where the program has minimal number of live registers. At run-time the preemption point is deferred to a switch point and the real-time operating system (RTOS) kernel invokes a switch point specific code generated by the compiler to save and restore the thread state in a custom fashion. Through the utilization of these novel mechanisms, a drastic improvement on both performance and response time is achieved. The presented experimental results demonstrate the effectiveness of the proposed technique on a number of widely-used computational kernels and embedded applications.