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RECAST: Boosting Tag Line Buffer Coverage in Low-Power High-Level Caches "for Free"
San Jose, California October 02-October 05
DOI Bookmark: http://doi.ieeecomputersociety.org/10.1109/ICCD.2005.902005 International Conference on Comp ...
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Won-Ho Park, Electrical and Computer Engineering, University of Toronto
Andreas Moshovos, Electrical and Computer Engineering, University of Toronto
Babak Falsafi, Electrical and Computer Engineering, Carnegie Mellon University

We revisit the idea of using small line buffers in-front of caches. We propose ReCast, a tiny tag set cache that filters a significant number of tag probes to the L2 tag array thus reducing power. The key contribution in ReCast is S-Shift, a simple indexing function (no logic involved just wires) that greatly improves the utility of line buffers with no additional hardware cost. S-Shift can be viewed as a technique for emulating larger cache blocks and hence exploiting more spatial locality but without paying the penalties of actually using a larger L2 cache block. Using several SPEC CPU2000 applications and a model of an aggressive, dynamicallyscheduled, superscalar processor we demonstrate that a practical ReCast organization can significantly reduce power in the L2. Specifically, a 64-entry ReCast comprising eight sub-banks of eight entries each can filter about 50% of all tag probes for a 1Mbyte L2 cache. A conventional line buffer of the same size filters only 32% of all tag probes. The resulting average reduction in L2 tag power is 38% and 85% with writeback or writethrough L1 caches respectively. This translates to a reduction of 16% or 52% of the overall L2 power respectively. We also analyze a few representative applications explaining why S-Shift works well.

Citation:
Won-Ho Park, Andreas Moshovos, Babak Falsafi, "RECAST: Boosting Tag Line Buffer Coverage in Low-Power High-Level Caches "for Free"," iccd, pp.609-616, 2005 International Conference on Computer Design, 2005
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