StimulusCache: Boosting performance of chip multiprocessors with excess cache

Technology advances continuously shrink on-chip devices. Consequently, the number of cores in a single chip multiprocessor (CMP) is expected to grow in coming years. Unfortunately, with smaller device size and greater integration, chip yield degrades significantly. Guaranteeing that all chip components function correctly leads to an unrealistically low yield. Chip vendors have adopted a design strategy to market partially functioning processor chips to combat this problem. The two major components in a multicore chip are compute cores and on-chip memory such as L2 cache. From the viewpoint of the chip yield, the compute cores have a much lower yield than the on-chip memory due to their logic complexity and well-established memory yield enhancing techniques. Therefore, future CMPs are expected to have more available on-chip memories than working cores. This paper introduces a novel on-chip memory utilization scheme called StimulusCache, which decouples the L2 caches of faulty compute cores and employs them to assist applications on other working cores. Our extensive experimental evaluation demonstrates that StimulusCache significantly improves the performance of both single-threaded and multithreaded workloads.