Data Sharing or Resource Contention: Toward Performance Transparency on Multicore Systems

Modern multicore platforms suffer from inefficiencies due to contention and communication caused by sharing resources or accessing shared data. In this paper, we demonstrate that information from low-cost hardware performance counters commonly available on modern processors is sufficient to identify and separate the causes of communication traffic and performance degradation. We have developed SAM, a Sharing-Aware Mapper that uses the aggregated coherence and bandwidth event counts to separate traffic caused by data sharing from that due to memory accesses. When these counts exceed pre-determined thresholds, SAM effects task to core assignments that colocate tasks that share data and distribute tasks with high demand for cache capacity and memory bandwidth. Our new mapping policies automatically improve execution speed by up to 72% for individual parallel applications compared to the default Linux scheduler, while reducing performance disparities across applications in multiprogrammed workloads.