SuperRange: Wide Operational Range Power Delivery Design for both STV and NTV Computing Xin He, Guihai Yan, Yinhe Han, Xiaowei Li Institute of Computing Technology, Chinese Academy of Sciences

Microprocessor’s supply voltage range has been gradually increasing in these year – Intel Pentium Processor has a supply voltage range from 0.9V to 1.5V to support DVFS – Intel Sandy Bridge Processor requires a higher than nominal voltage to boost performance The need of wide operation range 1 0.9V Intel Pentium Processor 1.5V Turbo Boost in Intel Sandy Bridge (66.7%)

– Near Threshold Computing: set supply voltage to a value near to transistor’s threshold voltage (0.4V- 0.6V) The need of wide operation range 2 Intel ISSCC V-1.2V Future Microprocessor has wide supply voltage range. Brings challenges to power delivery design

Voltage regulator is key to deliver power at a specified voltage level – Linear regulator-LDO – Switching regulator Buck regulator(Off-VR) Switch capacitor regulator(On-VR) Background of Power Delivery Design Buck RegulatorSwitch Capacitor Regulator

VRs are delivering power to wide operational range cores Power Conversion Efficiency Characteristics High PCE Low PCE Off-VR: – High switching loss On-VR: – Narrow optimal region LDO-VR: – Limited efficiency Conventional design can’t meet the need of wide voltage range

Explore the design space of wide operational range power delivery design Propose SuperRange, a wide operation range power delivery scheme Present a VR aware power management algorithm to maximize performance under given power budget Contribution

Explore three optional design 1.Off-VRs Two Off-VR evenly located 2.Off-VR + LDO-VR An Off-VR serves as an frontend 3.Off-VR + On-VR Off-VR delivers to STV and On-VR to NTV Design space exploration

Loss in Off-VRs Option 1 ： Off-VRs scheme Cross 10%

In LDO-VR – PCE is limited by the ratio of output voltage to input voltage PCE is lower than 30% when delivering to NTV region Option 2 ： LDO-VR scheme

Option 3 ： Off-VR + On-VR scheme

Off-VR + On-VR scheme

Multi-phase Off-VR provides an opportunity to improve load current, thus PCE get improved – Modern Off-VR can dynamically change number of working phases Decreasing the number of working phases would increase output ripple – 1.5uH inductor is big enough to reduce the ripple with acceptable area overhead Proposed SuperRange Design

Supporting STV – Voltage conversion to STV is performed by Off-VR Supporting NTV – Two step conversion. Off-VR sets to single working phase On-VR achieves further conversion(e.g. 3:1) SuperRange Overview

Maximize performance under given power budget – Find optimal core counts and VF setting VR aware power management algorithm PCE with varying load current – Although low voltage improve app power efficiency, it degrades the PCE More cores, Low voltageFew cores, High voltage

Algorithm

Target processor characteristics – Multicore processor consists 16 ALPHA cores which has 9 power state (1.2v, 1.9GHz), (1.1v, 1.7GHz), (1.0v, 1.5GHz)… (0.4v, 0.3GHz) – 32MB LLC, distribute directory-based MESI – On chip interconnection: mesh + router Voltage regulator model – Single topology (3 to 1) Switch capacitor voltage regulator – Buck voltage regulator like TI TPS Experimental Setup

Power Conversion Efficiency SuperRange combines the advantages of Off-VR and On-VR and exhibits high PCE over the entire voltage range SuperRange combines the advantages of Off-VR and On-VR and exhibits high PCE over the entire voltage range

Performance comparison in power-constrait system Comparison SuperRange outperforms LDO scheme by 50% and Off-VR scheme by 30% SuperRange outperforms LDO scheme by 50% and Off-VR scheme by 30%

Maximum achievable performance comparison under shrinking power budget Comparison On average, SuperRange achieve 52% and 170% higher PCE than Off-VR and LDO-VR scheme. On average, SuperRange achieve 52% and 170% higher PCE than Off-VR and LDO-VR scheme.

Power delivery design for wide operational range is an important issue Explore the optional power delivery design scheme The proposed SuperRange scheme achieves high PCE over the entire operational range Propose a VR aware power management algorithm Conclusion

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