Then an optimal scheduling strategy is achieved by selecting two machines satisfying condition to change their loads via reassigning their tasks under the heuristic of their mean load . methods of selecting machines and tasks are given in this paper to increase the throughput of the system and reduce the total waiting time 在开放动态的网格环境中，任务调度器试图优化系统的性能指标，如：最小化平均任务执行时间最大化一定周期内任务执行数等，以提高整个系统的性能，满足用户的各种qos需求。
