A Compile-Time Optimization Method for WCET Reduction in Real-Time Embedded Systems through Block Formation

Abstract

Compile-time optimizations play an important role in the efficient design of real-time embedded systems. Usually, compile-time optimizations are designed to reduce average-case execution time (ACET). While ACET is a main concern in high-performance computing systems, in real-time embedded systems, concerns are different and worst-case execution time (WCET) is much more important than ACET. Therefore, WCET reduction is more desirable than ACET reduction in many real-time embedded systems. In this article, we propose a compile-time optimization method aimed at reducing WCET in real-time embedded systems. In the proposed method, based on the predicated execution capability of embedded processors, program code blocks that are in the worst-case paths of the program are merged to increase instruction-level parallelism and opportunity for WCET reduction. The use of predicated execution enables merging code blocks from different worst-case paths that can be very effective in WCET reduction. The experimental results show that the proposed method can reduce WCET by up to 45% as compared to previous compile-time block formation methods. It is noteworthy that compared to previous works, while the proposed method usually achieves more WCET reduction, it has considerably less negative impact on ACET and code size.