Loop-Based Instruction Prefetching to Reduce the Worst-Case Execution Time

Estimating and optimizing worst-case execution time (WCET) is critical for hard real-time systems to ensure that different tasks can meet their respective deadlines. Recent work has shown that simple prefetching techniques such as the Next-N-Line prefetching can enhance both the average-case and worst-case performance; however, the improvement on the worst-case execution time is rather limited and inefficient. This paper studies a loop-based instruction prefetching approach, which can exploit the program control-flow information to intelligently prefetch instructions that are most likely needed. Our evaluation indicates that the loop-based instruction prefetching outperforms the Next-N-Line prefetching in both the worst-case and the average-case performance for real-time applications.

1 Introduction

Real-Time systems such as automobile and aircraft controllers have been widely used in our society. Besides performance, time predictability is also essential to these systems. Missing deadlines in those applications may either lead to catastrophic consequences or decrease quality of services. Consequently, it is important to know the worst-case execution time (WCET) of each task, which provides the basis for schedulability analysis in real-time systems, especially for hard real-time and safety-critical systems.