Cache Power Reduction in Presence of Within-Die Delay Variation Using Spare Ways

The share of leakage in cache power consumption increases with technology scaling. Choosing a higher threshold voltage (V_th) and/or gate-oxide thickness(T_ox) for cache transistors improves leakage, but impacts cell delay. We show that due to uncorrelated random within-die delay variation, only some (not all)of cells actually violate the cache delay after the above change. We propose to add a spare cache way to replace delay-violating cache-lines separately in each cache-set. By SPICE and gate-level simulations in a commercial 90 nm process, we show that choosing higher V_th, T_ox and adding one spare way to a 4-way 16 KB cache reduces leakage power by 42%, which depending on the share of leakage in total cache power, gives up to 22.59% and 41.37% reduction of total energy respectively in L1 instruction- and L2 unified-cache with a negligible delay penalty, but without sacrificing cache capacity or timing-yield.