Precise shared cache analysis using optimal interference placement

Determining the Worst Case Execution Time (WCET) of programs running on a multi-core architecture is a challenging problem, that is hampering the use of multi-cores in real-time systems. The highly imprecise WCET estimates obtained using the current state-of-the-art analyses has prompted research in the direction of making the multi-core architecture itself more estimation-friendly, but there has been little effort to make the WCET analysis more precise. The main difficulty in analyzing programs running on multi-core architectures arises from the fact that interferences to shared resources (such as shared cache) from other cores can occur at any time. Hence, to perform safe micro-architectural analysis, current approaches assume that all interferences occur at all times, which results in significantly imprecise analysis WCET estimates. However, since we are interested in the WCET, we can instead assume that the interferences will come at the worst possible program points, causing maximum increase in the execution time. In our work, we formulate an ILP problem to determine these worst case interference points, from the perspective of a shared cache, and determine the WCET by assuming that the interferences come at those program points. Our approach provides an average precision improvement of 25.63% over earlier analysis for benchmarks which perform a reasonable number of accesses to the shared cache.