Dynamic fine-grain leakage reduction using leakage-biased bitlines

  • Authors:
  • Seongmoo Heo;Kenneth Barr;Mark Hampton;Krste Asanović

  • Affiliations:
  • MIT Laboratory for Computer Science, Cambridge, MA;MIT Laboratory for Computer Science, Cambridge, MA;MIT Laboratory for Computer Science, Cambridge, MA;MIT Laboratory for Computer Science, Cambridge, MA

  • Venue:
  • ISCA '02 Proceedings of the 29th annual international symposium on Computer architecture
  • Year:
  • 2002

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Abstract

Leakage power is dominated by critical paths, and hence dynamic deactivation of fast transistors can yield large savings. We introduce metrics for comparing fine-grain dynamic deactivation techniques that include the effects of deactivation energy and startup latencies, as well as long-term leakage current. We present a new circuit-level technique for leakage current reduction, leakage-biased bitlines, that has low deactivation energy and fast wakeup times. We show how this technique can be applied at a fine grain within an active microprocessor, and how microarchitectural scheduling policies can improve its performance. Using leakage-biased bitlines to deactivate SRAM read paths within I-cache memories saves over 24% of leakage energy and 22% of total I-cache energy when using a 70nm process. In the register file, fine-grained read port deactivation saves nearly 50% of leakage energy and 22% of total energy. Independently, turning off idle register file subbanks saves over 67% of leakage energy (57% total register file energy) with no loss in performance.