Control Techniques for Uncore Power Mangement in Chip Multiprocessor Designs

Abstract

In chip-multiprocessor (CMP) designs, when the number of core increases, the size of on-chip communication fabric and data storage grows accordingly and therefore the chip power challenge is exacerbated. This thesis work considers the power management for networks-on-chip (NoC) and the last level cache, which constitute the uncore in CMP designs. NoC is regarded as a scalable approach to cope with the increasing demand for on-chip communication bandwidth. The last level cache is shared among all cores. The focus of this work is on the control techniques for uncore dynamic voltage and frequency scaling. A realistic but not well-studied scenario is investigated. That is, the entire uncore shares a single voltage/frequency domain, as opposed to separated domains in most of previous works. One appealing advantage here is that data packets no longer experience the interfacing overhead across different voltage/frequency domains. The classic PI (Proportional and Integral) control method is adopted due to its simplicity, flexibility and low implementation overhead. This thesis research outcome includes three parts. First, stability of the PI control is analyzed. Second, a model-assisted PI control scheme is proposed and studied. The model assist is to address the problem that no universally good reference point exists for the control. Third, the windup issue for the PI control is investigated. Full architecture simulations are performed on public benchmark suites to validate the proposed techniques. The result show 76% energy reduction with less than 6% performance degradation compared to constantly high voltage/frequency for uncore.