Optimizing a Reconfigurable Power Distribution Network in a Multicore Platform

The emerging trend toward utilizing chip multicore processors (CMPs) that support dynamic voltage and frequency scaling (DVFS) is driven by user requirements for high performance and low power. To overcome limitations of the conventional chip-wide DVFS and achieve the maximum possible energy saving, per-core DVFS is being enabled in the recent CMP offerings. While power consumed by the CMP is reduced by per-core DVFS, power dissipated by the set of voltage regulators (VRs) that are required to support per-core DVFS becomes critical. This paper focuses on the dynamic control of the VRs in a CMP platform. Starting with a proposed platform with a reconfigurable VR-to-core power distribution network (PDN), two optimization methods are presented to maximize the system-wide energy savings: 1) reactive VR consolidation (VRCon) to reconfigure the network for maximizing the power conversion efficiency of the VRs, which is performed under the predetermined DVFS levels for the cores and 2) proactive VRCon to determine new DVFS levels for maximizing the total energy savings without any performance degradation. Along with the optimization methods for the PDN composed of homogeneous VRs, we also discuss the PDN with heterogeneous VRs, which is proposed to increase the benefits of the VRCon by incorporating VRs with a larger driving capability of load current. Results from detailed simulations based on realistic experimental setups demonstrate up to 36% VR energy loss reduction and 9% total energy saving.