Selective Writeback: Improving Processor Performance and Energy-Efficiency

* Oguz Ergin is currently with Intel Labs Barcelona, Spain. Abstract A significant fraction of the result values in today's superscalar microprocessors are delivered to their consumers via forwarding and are never read out from the destination registers. Such transient values are kept in the register file solely for the purpose of recovering the processor state on interrupts or exceptions. In this paper, we propose a simple technique to identify such transient register values and avoid their writebacks into the register file. Our scheme results in significant performance improvement, as high as 40% for some benchmarks and 12% on the average because the register file is utilized more efficiently. Energy savings of 27% within the register file are also achieved because much fewer writes to the register file are performed.