一种面向实时系统的程序基本块指令预取技术

面向通用计算机系统的指令预取技术无法满足实时系统的应用需求，其中一个重要原因是：无效预取引起的指令Cache内容污染使得实时任务WCET评估值不够精确，导致系统可调度性下降，严重影响系统效率.以简化实时任务WCET分析、降低任务WCET评估值为目标，提出一种基于程序基本块的指令预取方法.该方法以基本块为粒度执行指令预取，避免了传统指令预取技术引入的无效预取；通过简化最坏情况下的指令访问命中/缺失情况判定，简化任务WCET分析过程并优化WCET评估值.实时基准测试程序评估结果表明：与常规无预取方法相比，该预取方法可使实时任务WCET评估值降低约20%，平均执行情况下的指令Cache访问性能提升约10%.

Basic-Block Based Instruction Prefetching Technology for Real-Time System

Instruction prefetching technologies proposed for general purpose computer systems cannot meet the requirements of real- time systems. One of the most important issues is that cache content pollution caused by useless prefetching loses real-time tasks'' WCET estimates. And a loose on WCET analysis degrades the schedulability of the system and in turn brings down its efficiency. A basic-block based instruction prefetching method is proposed in this paper. The method performs instruction prefetching at the basic block level, avoids useless prefetching, simplifies the instruction hit/miss classifications in the worst-case execution, and reduces the WCET estimates of real-time tasks. Real-time benchmark tests show that, the method can reduce real-time tasks'' WCET estimates by 20% and also improve instruction cache access performance by 10% on average.