Taking Advantage of Within-Die Delay-Variation to Reduce Cache Leakage Power Using Additional Cache-Ways

4th International Workshop on Dependable Embedded Systems : October 9, 2007 : Beijing, ChinaLeakage power, especially in cache memories, is dominating total power consumption of processor-based embedded systems. By choosing a higher threshold voltage, SRAM leakage can be exponentially reduced in return for lower speed. Since SRAM cells in the same cache have different delays in nanometer technologies due to within-die process variation, not all of the cells violate the cache delay. However, since timing-violating cells are randomly distributed over the cache, row/column redundancies are inefficient. We propose to add extra cache-way(s) to replace slow cache-lines separately in each cache-set. In a commercial 90nm process, our technique can reduce leakage power by up to 54% which, depending on the share of leakage in total cache power, translates to 25.36% and 53.37% reduction of total energy respectively in L1 and L2 cache by adding two spare ways to a 4-way set-associative cache with no performance penalty