Asymmetric Real-time Scheduling Algorithm Research Based On Xen

In recent years, with the continuous development of virtualization technology, in particular the chip manufacturer to provide more and more hardware support, the embedded virtualization has a solid foundation. The embedded virtualization technology is mainly adopted in mobile communication and industry control. The operating systems used in the industry control have strong demand for real-time. In the past, a big system was constructed by several real-time control subsystems and the subsystem runs at independent hardware platform. Thus, these subsystems could be co-running at a multiprocessor platform by the embedded virtualization technology as well as cut down device and maintenance cost without sacrifice performance and influence real-time response time. The subsystems could run without influence others; the stability, reliability and security are guaranteed. A general purpose operating system like Windows XP or Linux also be able to run at the same hardware platform to supply a friendly human interface.One of the virtualization technology's features is support many operating systems to run at the same time. The virtualization platform needs to allocate CPU time slice to these operating systems reasonable and effectively for they are co-running at the same hardware platform. Thus the algorithm to allocate CPU time slice is called virtual machine scheduling algorithm.Nowadays, the popular virtualization platform including VMWare, Virtual PC, KVM and Xen could not support real-time virtual machine well. And the Xen platform's Credit Scheduler allocates CPU time slice fairly and efficiently. According the Credit value of different virtual machines, it divided them into three priorities: under, over and idle. The virtual machines could be at three states: boost, running and block. Also the scheduler could ensure the virtual machines to share the CPU fairly, but it could not be able to guarantee the real-time performance of real-time virtual machines.Based on in-depth research and analysis on Xen's Credit scheduler, this paper presents an improved asymmetric real-time scheduling algorithm. The asymmetric real-time scheduling algorithm is featured with real-time guest friendly, real-time event driven mechanism and multiple real-time guests balancing method. The real-time guest's event latency is cut down effectively and the real-time performance is improved. And the real-time performance shaking that caused by preemption recurrence between real-time guests is eliminated by the multiple real-time guests balancing method. The experiment results show that the real-time performance of the real-time guests in Xen is enhanced effectively.