Guaranteeing Hits to Improve the Efficiency of a Small Instruction Cache

  • Authors:
  • Stephen Hines;David Whalley;Gary Tyson

  • Affiliations:
  • -;-;-

  • Venue:
  • Proceedings of the 40th Annual IEEE/ACM International Symposium on Microarchitecture
  • Year:
  • 2007

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Abstract

Very small instruction caches have been shown to greatly reduce fetch energy. However, for many appli- cations the use of a small filter cache can lead to an unacceptable increase in execution time. In this paper, we propose the Tagless Hit Instruction Cache (TH-IC), a technique for completely eliminating the performance penalty associated with filter caches, as well as a fur- ther reduction in energy consumption due to not having to access the tag array on cache hits. Using a few meta- data bits per line, we are able to more efficiently track the cache contents and guarantee when hits will occur in our small TH-IC. When a hit is not guaranteed, we can instead fetch directly from the L1 instruction cache, eliminating any additional cycles due to a TH-IC miss. Experimental results show that the overall processor en- ergy consumption can be significantly reduced due to the faster application running time and the elimination of tag comparisons for most of the accesses.