Modifying the Data-Holding Components of the Microprocessors for Energy Efficiency

Abstract

Storage components are a major source of energy dissipation in modern superscalar microprocessors. As the instruction windows get larger with each generation of processors, register files and other structures that hold intermediate data become larger and dissipate more power. Therefore it is important to find new ways to reduce the energy dissipation of data holding components. Many values written to and read from these storage components are known to require fewer bits than is provided by the storage space. Upper order bits of these values are unnecessary and energy savings can be achieved by not writing and reading these bits. Floating value data has different characteristics and offer special energy savings opportunities. In this paper we analyze the bit-level statistics of data values and propose simple modifications to data holding components that save significant energy inside the processors. Our results show that by using simple modifications on the storage components it is possible to achieve 40% reduction in the integer register file energy dissipation and up to 60% reduction in the immediate field of the issue queue. We also show that energy dissipation can be reduced by half for some floating point benchmarks by identifying values that indicate a zero operand.