Scheduling overcommitted VM: Behavior monitoring and dynamic switching-frequency scaling

Virtualization enables multiple guest operating systems run on a single physical platform. These virtual machines (i.e., VM) may host any type of application, including concurrent HPC programs. Traditionally, VMM schedulers have focused on fairly sharing the processor resources among VMs, rarely consider VCPUs' behaviors. However, this can result in poor application performance to overcommitted virtual machines if there are concurrent programs hosted in them. In this paper, we review the features 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 VMs. We discuss the origination of the problem theoretically, and confirm the derived conclusion on benchmarks. A novel approach is then proposed to improve the Credit scheduler, more adaptive for concurrent applications. Our solution includes two aspects: a periodical monitor analyzing the behaviors of each VCPU in a real-time manner, and the scheduler (extended from Credit scheduler) dynamically scaling the context switching-frequency by applying variable time slices to VCPUs according to their behaviors. The experimental results show that this extended Credit scheduler can significantly improve the performance of communication-intensive and I/O-intensive concurrent applications in overcommitted VMs, which is as good as the performance in undercommitted scenarios. Highlights? Performance decreases dramatically in overcommitted domains with Xen's Credit scheduler. ? We analyze the root cause of this performance problem theoretically. ? We propose a solution based on behavior monitoring and dynamic switching-frequency scaling. ? Our solution can combine the advantages of both Credit and SEDF schedulers.