Multi-core architectures with asymmetric core performance have recently shown great promise, because applications with different needs can benefit from either the high performance of a fast core or the high parallelism and power efficiency of a group of slow cores. This performance heterogeneity can be particularly beneficial to applications running in virtual machines (VMs) on virtualized servers, which often have different needs and exhibit different performance and power characteristics. Therefore, scheduling VMs on performance-asymmetric multicore architectures can have a great impact on a system's overall energy efficiency. Unfortunately, existing VM managers, such as Xen, have not taken the heterogeneity into account and thus often result in low energy efficiencies. In this paper, we propose a novel VM scheduling algorithm that exploits core performance heterogeneity to optimize the overall system energy efficiency. We first introduce a metric termed energy-efficiency factor to characterize the power and performance behaviors of the applications hosted by VMs on different cores.We then present a method to dynamically estimate the VM's energy-efficiency factors and then map the VMs to heterogeneous cores, such that the energy efficiency of the entire system is maximized. We implement the proposed algorithm in Xen and evaluate it with standard benchmarks on a real testbed. The experimental results show that our solution improves the system energy efficiency (i.e., performance per watt) by 13.5% on average and up to 55% for some benchmarks, compared to the default Xen scheduler.
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