Abstract: The two scheduling algorithms released by Xen4. 1 neither get good performance in multitask virtualization on server. After analyzing the characteristic and requirements of three types of tasks running on virtual machines,optimization methods were proposed;sorting I/O tasks by consumed time,preferably scheduling I/O task of less consumed time, recording computing-mode task associated with the cache to maintain cache consistency. Thereby we improved the cache efficiency on the basis of ensuring the I/O response and bandwidth performance.

Key words: Multitask virtualization, Cache efficiency, Scheduling optimization, Xen