Dynamic Switching-Frequency Scaling: Scheduling Overcommitted Domains in Xen VMM

Virtualization enables multiple guest operating systems run on a single physical platform. These virtual machines may host any types of application, including concurrent HPC programs. Traditionally, VMM schedulers have focused on fairly sharing the processor resources among domains, rarely consider VCPUs´ behaviors. However, this can result in poor application performance to overcommitted domains if there are concurrent programs hosted in them. In this paper we review the properties of both Xen´s Credit and SEDF schedulers, and show how these schedulers may seriously impact the performance of the communication-intensive and I/O-intensive concurrent applications in overcommitted domains. We discuss the origination of the problem theoretically, and confirm the derived conclusion on benchmarks. A novel approach, that dynamically scales the context switching-frequency by selecting variable time slices according to VCPUs` behaviors, is then proposed to improve the Credit scheduler more adaptive for concurrent applications. The experimental results show that this extended Credit scheduler can improve the performance of communication-intensive and I/O-intensive concurrent applications in overcommitted domains to the same magnitude as in undercommitted domains.