On the assessment of probabilistic WCET estimates reliability for arbitrary programs

Abstract

Measurement-Based Probabilistic Timing Analysis (MBPTA) has been shown to be an industrially viable method to estimate the Worst-Case Execution Time (WCET) of real-time programs running on processors including several high-performance features. MBPTA requires hardware/software support so that program’s execution time, and so its WCET, has a probabilistic behaviour and can be modelled with probabilistic and statistic methods. MBPTA also requires that those events with high impact on execution time are properly captured in the (R) runs made at analysis time. Thus, a representativeness argument is needed to provide evidence that those events have been captured. This paper addresses the MBPTA representativeness problems caused by set-associative caches and presents a novel representativeness validation method (ReVS) for cache placement. Building on cache simulation, ReVS explores the probability and impact (miss count) of those cache placements that can occur during operation. ReVS determines the number of runs R ', which can be higher than R, such that those cache placements with the highest impact are effectively observed in the analysis runs, and hence, MBPTA can be reliably applied to estimate the WCET.