The BubbleWrap many-core: Popping cores for sequential acceleration

Many-core scaling now faces a power wall. The gap between the number of cores that fit on a die and the number that can operate simultaneously under the power budget is rapidly increasing with technology scaling. In future designs, many of the cores may have to be dormant at any given time to meet the power budget. To push back the many-core power wall, this paper proposes Dynamic Voltage Scaling for Aging Management (DVSAM) - - a new scheme for managing processor aging to attain higher performance or lower power consumption. In addition, this paper introduces the BubbleWrap many-core, a novel architecture that makes extensive use of DVSAM. BubbleWrap identifies the most power-efficient set of cores in a variation-affected chip - - the largest set that can be simultaneously powered-on - - and designates them as Throughput cores dedicated to parallel-section execution. The rest of the cores are designated as Expendable and are dedicated to accelerating sequential sections. BubbleWrap attains maximum sequential acceleration by sacrificing Expendable cores one at a time, running them at elevated supply voltage for a significantly shorter service life each, until they completely wear-out and are discarded - - figuratively, as if popping bubbles in bubble wrap that protects Throughput cores. In simulated 32-core chips, BubbleWrap provides substantial improvements over a plain chip. For example, on average, one design runs fully-sequential applications at a 16% higher frequency, and fully-parallel ones with a 30% higher throughput.