中文摘要：

针对需要精确地评估分析云数据中心服务性能以保证服务质量（QoS）和避免违反服务水平协议（SLA）的问题,提出了一个基于M/M/n/n＋r排队系统云计算中心近似分析模型.通过求解该模型获得用户请求响应时间的分布函数以及其他重要的QoS性能指标,同时通过仿真实验验证和获得服务器数量、队列缓冲区大小与响应时间、请求阻塞概率以及请求立即服务概率之间的关系.实验结果表明,提高服务器服务速率比增加服务器数量更利于提高服务性能.

英文摘要：

Since it is necessary to evaluate and analyze the service performance of cloud computing center to guarantee Quality of Service （QoS） and avoid violation of Service Layer Agreement （SLA）, a approximated analysis model based on M/ M/n/n ＋ r queue theory was proposed for cloud computing center. By solving this model the probability distribution function of response time and other QoS indicators were acquired, meanwhile the relationship among the number of servers, size of queue buffers, response time, blocking probability and instance service probability were revealed and verified by simulation. The experimental results indicate that improving server service rate is better than increasing the number of servers for improving service performance.