Optimal sleeping: models and experiments for energy-delay tradeoff

ABSTRACTMulti-core architectures have supplanted single core schemes, in part because the maximum clock speed of a single core is limited by its energy consumption. They provide the additional, less exploited benefit of allowing a finer trade-ff between energy consumption and delay by turning off subsets of cores. We investigate how this tradeoff varies with the number of cores, and whether heterogeneity brings additional benefits to outweigh its increased complexity. We study optimal sleep policies in two settings: switching of homogeneous cores on a fast timescale, which models multiple cores in a CPU, and switching of heterogeneous cores on a slow timescale, which models different generation servers in a data centre. In the homogeneous-core case, we show the optimal policy is monotone hysteretic, and that the performance is less sensitive to load estimation errors. By implementing this policy on a real experimental testbed, we show that theory makes a good prediction of the resource pooling benefits, a...