Under the “customer who is charged takes the priority” principle, the high priority customers of a many-processor multitask cloud service system rapidly increase. That is, the possibility of the intensiveness saturated event of high priority customer will greatly improve. Under this circumstance, to ensure the Qos of the system becomes the key point the the ISSA layer. FIFO algorithm is relatively simple, but to ensure Qos system, it still need to make advantage of the existed Hierarchical Weighted Algorithm(HWA) to initially realize. While based on the high priority customer feature of intensiveness, HWA will gradually become FIFO-like service model and then decrease Qos. Our goal is, under the circumstance of the intensive request of high priority customer in the IAAS layer, to ensure the request of high priority customer and meanwhile prevent the increase of high priority customer from becoming FIFO-like service model which will decrease Qos, thus to ensure the stability of the system. Therefore a Composite Weighted Scheduling Algorithm(CWSA) which is based on system stability is put forward. Compared with FIFO and HWA, the simulation result shows that under the circumstances of intensive request of high priority, the system throughput and average occupancy of this kind of scheduling algorithm are both greatly improved. While the packet loss probability makes no big difference, Qos could be ensured better, that is the system stability could be ensured better.
