FlexWatts: A Power- and Workload-Aware Hybrid Power Delivery Network for Energy-Efficient Microprocessors

Abstract

Modern client processors typically use one of three commonlyused power delivery network (PDN) architectures: 1) motherboard voltage regulators (MBVR), 2) integrated voltage regulators (IVR), and 3) low dropout voltage regulators (LDO). We observe that the energy-e ciency of each of these PDNs varies with the processor power (e.g., thermal design power (TDP) and dynamic power-state) and workload characteristics (e.g., workload type and computational intensity). This leads to energyine ciency and performance loss, as modern client processors operate across a wide spectrum of power consumption and execute a wide variety of workloads.To address this ine ciency, we propose FlexWatts, a hybrid adaptive PDN for modern client processors whose goal is to provide high energy-e ciency across the processor's wide range of power consumption and workloads. FlexWatts provides high energy-e ciency by intelligently and dynamically allocating PDNs to processor domains depending on the processor's power consumption and workload. FlexWatts is based on three key ideas. First, FlexWatts combines IVRs and LDOs in a novel way to share multiple on-chip and o -chip resources and thus reduce cost, as well as board and die area overheads. This hybrid PDN is allocated for processor domains with a wide power consumption range (e.g., CPU cores and graphics engines) and it dynamically switches between two modes: IVR-Mode and LDO-Mode, depending on the power consumption. Second, for all other processor domains (that have a low and narrow power range, e.g., the IO domain), FlexWatts statically allocates o -chip VRs, which have high energy-e ciency for low and narrow power ranges. Third, FlexWatts introduces a novel prediction algorithm that automatically switches the hybrid PDN to the mode (IVR-Mode or LDO-Mode) that is the most bene cial based on processor power consumption and workload characteristics.