Software-Level Memory Regulation to Reduce Execution Time Variation on Multicore Real-Time Systems

Modern real-time embedded systems are equipped with multi-core processors to execute computationally intensive tasks. In multi-core architecture, last-level cache memory is shared by cores. The shared cache becomes a non-deterministic resource, which affects the independent execution of real-time tasks. We propose a solution to remedy a variation in execution time when interference happens in a shared cache. Current solutions have relied on memory scheduling approaches that avoid concurrent memory access to guarantee deterministic execution time. However, these methods required complex analysis to accurately estimate the worst-case execution time and to schedule tasks in an overly conservative manner. Unlike existing works, the proposed method prevents simultaneous memory access using the side effect of memory barriers rather than the complicated analysis. A memory barrier is inserted based on a simple code analysis that is performed in units of basic blocks using the LLVM compiler. The proposed method not only does not require the modification of the operating system or task execution flow but also relatively shows fast analysis time. To verify the proposed method, we compared the standard deviation of the execution time of each core in a situation where shared cache interference occurs in multi-core. Experimental results show that the proposed basic block-based memory barrier insertion method can reduce the variation in execution time by up to 80% when interference occurs.