1. A method implemented on at least one machine each having at least one processor, storage, and a communication platform connected to a network for dynamic control of a processing system having a plurality of tiers, the method comprising: obtaining queue lengths of a plurality of nodes in one of the plurality of tiers; receiving a control objective from a higher tier, wherein one or more requests from the higher tier are processed by the plurality of nodes in the tier; computing a control model of the tier based on the received queue lengths, wherein one or more parameters of the control model are adjusted based on the received control objective; and determining at least one control action based on the control mode and the control objective.