A defect-aware reconfigurable cache architecture for low-vccmin DVFS-enabled systems

As process technology continues to shrink, a large number of bitcells in on-chip caches is expected to be faulty. The number of defective cells varies from die-to-die, wafer-to-wafer, and in the field of application depends on the run-time operating conditions (e.g., supply voltage and frequency). Those trends necessitate i) to study fault-tolerant (FT) cache mechanisms in a wide spectrum of fault-probabilities and ii) to devise appropriate FT techniques that must be able to adapt their FT capacity to the volume of defective locations of the target faulty caches.

It is well known that keeping the cache capacity, block size and the volume of defective cells constant, the average number of misses, due to faulty cells, decreases as the associativity of the cache increases. To this end, we propose DARCA, a Defect-Aware Reconfigurable Cache Architecture, which is equipped with the ability of dynamically varying its associativity according to the volume of defective cells. To keep the hardware overhead very small, as the associativity of the cache is multiplied by a power of two, its block size is divided by the same number. Since almost all contemporary processors use prefetching, we also applied DARCA to prefetch-assisted caches. By performing cycle-accurate simulations for the SPEC2006 benchmarks assuming a wide range of fault-probabilities, we show that DARCA compares favorably against several known FT cache mechanisms with respect to the performance loss caused by defective cells.