Resilience Analysis: Tightening the CRPD bound for set-associative caches

In preemptive real-time systems, scheduling analyses need-in addition to the worst-case execution time-the context-switch cost. In case of preemption, the preempted and the preempting task may interfere on the cache memory. This interference leads to additional cache misses in the preempted task. The delay due to these cache misses is referred to as the cache-related preemption delay (CRPD), which constitutes the major part of the context-switch cost. In this paper, we present a new approach to compute tight bounds on the CRPD for LRU set-associative caches, based on analyses of both the preempted and the preempting task. Previous approaches analyzing both the preempted and the preempting task were either imprecise or unsound. As the basis of our approach we introduce the notion of resilience: The resilience of a memory block of the preempted task is the maximal number of memory accesses a preempting task could perform without causing an additional miss to this block. By computing lower bounds on the resilience of blocks and an upper bound on the number of accesses by a preempting task, one can guarantee that some blocks may not contribute to the CRPD. The CRPD analysis based on resilience considerably outperforms previous approaches.