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 obtained queue lengths of the tier, wherein one or more parameters of the control model are automatically optimized based on the received control objective from the higher tier; and determining at least one control action based on the control mode and the control objective, wherein the steps of obtaining, receiving, computing, and determining are performed in the tier at a frequency that is determined based on a number of control actions available to the processing system per unit of time and that is higher than a frequency at which the steps of obtaining, receiving, computing, and determining are performed in the higher tier.