Preserving I/O prioritization in virtualized OSes

While virtualization helps to enable multi-tenancy in data centers, it introduces new challenges to the resource management in traditional OSes. We find that one important design in an OS, prioritizing interactive and I/O-bound workloads, can become ineffective in a virtualized OS. Resource multiplexing between multiple tenants breaks the assumption of continuous CPU availability in physical systems and causes two types of priority inversions in virtualized OSes. In this paper, we present xBalloon, a lightweight approach to preserving I/O prioritization. It uses a balloon process in the virtualized OS to avoid priority inversion in both short-term and long-term scheduling. Experiments in a local Xen environment and Amazon EC2 show that xBalloon improves I/O performance in a recent Linux kernel by as much as 136% on network throughput, 95% on disk throughput, and 125x on network tail latency.