CAP: Color-aware task partitioning for multicore real-time applications

Modern multicore platforms feature multiple levels of cache memory placed between the processor and main memory to hide the latency of ordinary memory systems. The primary goal of this cache hierarchy is to improve average execution time (at the cost of predictability). The uncontrolled use of the cache hierarchy by real-time tasks may impact the estimation of their worst-case execution times (WCET). Software cache partitioning through page coloring has been considered a promising approach to isolate task workloads and thus improve WCET estimation. However, when real-time tasks share cache partitions due to false or true sharing, the inter-core delay caused by the cache coherence protocol may cause deadline losses. In this paper, we propose a Color-Aware task Partitioning (CAP) algorithm that assigns tasks to cores respecting their usage of cache partitions (i.e., colors). Tasks that share one or more colors are grouped together and the whole group is assigned to the same processor. Thus, it is possible to avoid inter-core interference. We compared the deadline miss ratio of several generated task sets partitioned by the CAP algorithm and by the worst-fit decreasing heuristic. We executed the partitioned task sets in a modern 8-core processor with shared L3-cache using a real-time operating system. Our results indicate that a color-aware task partitioning algorithm can avoid deadline misses in a multicore processor with shared cache.