Adaptive audio-aware scheduling in Xen virtual environment

With the development of client virtualization technology, it has become an important tendency to apply soft real-time applications in virtual environment. Currently, most schedulers in VMM (i.e., virtual machine monitor) take the fairly sharing of processor resources and load balancing as a main concern, while show less regard to application diversity and I/O responsiveness. This would be unable to meet the requirement for latency-sensitive tasks, such as audio application. Audio stream may suffer from severe input buffer overrun or output buffer underrun, especially in the case that there is no real-time guarantee on virtualized clients under heavy load. In this paper, we introduce experiments to illustrate that current scheduler in Xen does a poor job in guaranteeing fluent audio playing, and then formulate the fluent playing conditions a scheduler should satisfy. A scheduling strategy with soft real-time support is proposed to improve the responsiveness of latency-sensitive guests. To implement our proposition, we extend the Credit scheduler by using flexible time slice and real-time priority. Our solution is audio-aware and capable of adjusting the real-time priority of guest domains adaptively, achieving a better experience for end-users. The experimental results show that audio glitches can be completely eliminated via our extended scheduler even when the system load is very high.