A runtime support mechanism for fast mode switching of a self-morphing core for power efficiency

Abstract

Asymmetric multicore processors (AMPs) consist of cores executing the same ISA, but differing in microarchitectural resources, performance, and power consumption. As the computational bottleneck of a workload shifts from one resource to the next, during its course of execution, reassigning it to the core where it runs most efficiently can improve the overall energy efficiency. Simulation studies show that the performance bottlenecks can shift frequently, often within a few thousands cycles. With frequent core hooping, the overhead of thread migration becomes significant. To mitigate this overhead, we propose a morphable core that can assume one of four possible configurations to address the dominant performance bottlenecks, while retaining the same cache and registers. This way the architectural state remains intact while the morphable core is reconfigured in resources and frequency. We then implement a runtime scheme to decide the best configuration to run on and switch configuration as necessary. Simulation results indicate that on the average, the proposed scheme results in performance/watt improvement of 41%.