Address-Independent Estimation of the Worst-Case Memory Performance

Real-time systems are subject to temporal constraints and require a schedulability analysis to ensure that task execution finishes within lower and upper specified bounds. Worst-case memory performance (WCMP) plays a key role in the calculation of the upper bound of the execution time. Data caches complicate the calculation of the WCMP, since their behavior is highly dependent on the sequence of memory addresses accessed, which is often not available. For example, the address of a data structure may not be available at compile-time, and it may change between different executions of the program. We present an analytical model that provides fast, safe and tight estimations of the WCMP component of the worst-case execution time, using no information about the data base addresses. The address-independent absolute WCMP for codes with references that follow the same access pattern can be very high with respect to the average behavior because those references may be aligned with respect to the cache, thus generating systematic interferences among them. Our model can also provide a tighter and safe estimation for the WCMP for these codes when the user avoids these alignments.