Fine-grained QoS scheduling for PCM-based main memory systems

With wide adoption of chip multiprocessors (CMPs) in modern computers, there is an increasing demand for large capacity main memory systems. The emerging PCM (Phase Change Memory) technology has unique power and scalability advantages and is regarded as a promising candidate among new memory technologies. When scheduling a mix of applications of different priority levels, it is often important to provide tunable QoS (Quality-of-Service) for the applications with high priority. However due to the slow PCM cell access, and the destructive interferences among concurrent applications, existing memory scheduling schemes lack the flexibility to tune QoS in a wide range, in particular to the level close or equal to that of standalone execution. In this paper we propose a novel QoS scheduling scheme that utilizes request preemption and row buffer partition that enable QoS tuning at a fine-granularity. That is, they can tune the request queuing time and the PCM bank service time for the high priority requests. Our experimental results show that the proposed scheme achieves 1.7× ~10× QoS tuning range while introducing negligible area and energy overheads.