Dynamic indexing: Concurrent leakage and aging optimization for caches

Previous works have shown that the traditional implementations of power management (i.e., using power gating or voltage scaling) can also mitigate the aging effect induced by Negative Bias Temperature Instability (NBTI), due to the partial recovery that occurs during the idle intervals used by power management. However, such a potential has been exploited only partially because of the different nature of energy and aging: as a performance figure, aging is affected by the worst idleness pattern. Therefore, large potential energy savings usually turn into limited aging reductions. We address this problem in the context of caches, for which idleness is related to their access pattern. We propose a dynamic indexing scheme, in which the cache indexing function is changed over time in order to uniformly distribute the idleness over all the cache lines. In this way it is possible to fully use the leakage optimization potential and to extend the lifetime of a cache. Experimental analysis shows that it is possible to obtain caches that are effectively aging-free, without any penalty in leakage energy reduction.