Pilot Register File: Energy Efficient Partitioned Register File for GPUs

摘要

GPU adoption for general purpose computing hasbeen accelerating. To support a large number of concurrentlyactive threads, GPUs are provisioned with a very large registerfile (RF). The RF power consumption is a critical concern. Oneoption to reduce the power consumption dramatically is touse near-threshold voltage(NTV) to operate the RF. However, operating MOSFET devices at NTV is fraught with stabilityand reliability concerns. The adoption of FinFET devices inchip industry is providing a promising path to operate theRF at NTV while satisfactorily tackling the stability andreliability concerns. However, the fundamental problem of NTVoperation, namely slow access latency, remains. To tackle thischallenge in this paper we propose to build a partitioned RFusing FinFET technology. The partitioned RF design exploitsour observation that applications exhibit strong preference toutilize a small subset of their registers. One way to exploitthis behavior is to cache the RF content as has been proposedin recent works. However, caching leads to unnecessary areaoverheads since a fraction of the RF must be replicated. Furthermore, we show that caching is not efficient as weincrease the number of issued instructions per cycle, which isthe expected trend in GPU designs. The proposed partitionedRF splits the registers into two partitions: the highly accessedregisters are stored in a small RF that switches betweenhigh and low power modes. We use the FinFET's back gatecontrol to provide low overhead switching between the twopower modes. The remaining registers are stored in a largeRF partition that always operates at NTV. The assignment ofthe registers to the two partitions will be based on statisticscollected by the a hybrid profiling technique that combines thecompiler based profiling and the pilot warp profiling techniqueproposed in this paper. The partitioned FinFET RF is able tosave 39% and 54% of the RF leakage and the dynamic energy, respectively, and suffers less than 2% performance overhead.