Precise and scalable shared cache contention analysis for WCET estimation

Worst-Case Execution Time (WCET) analysis for real-time tasks must precisely predict cache hit/miss of memory accesses. While bringing great performance benefits, multi-core processors significantly complicate the cache analysis problem due to the shared cache contentions among different cores. Existing methods pessimistically consider that memory references of parallel executing tasks will contend with each other as long as they are mapped to the same cache line. However, in reality, numerous shared cache contentions are mutually exclusive, due to the partial orders among the programs executed in parallel. The presence of shared cache contentions greatly exacerbates the computational complexity of the WCET computation, as finding the longest path needs exploring an exponentially large partial ordering space. In this paper, we propose a quantitative method with O(n²) time complexity to precisely estimate the worst-case extra execution time (WCEET) caused by shared cache contentions. The proposed method can be easily integrated into the abstract-interpretation based WCET estimation framework. Experiments with MRTC benchmarks show that our method can averagely tighten the WCET estimation by 13% without sacrificing the analysis efficiency.