Modern network processor systems require the ability to adapt their processing capabilities at runtime to changes in network traffic. Traditionally, network processor applications have been optimized for a single static workload scenario, but recently several approaches for runtime adaptation have been proposed. Comparing these approaches and developing novel runtime support algorithms is difficult due to the multicore system-on-a-chip nature of network processors. In this paper, we present a model for network processors that can aid in evaluating different runtime support systems. The model considers workload characteristics of applications and network traffic using a queuork abstraction. The accuracy of this analytical approach to modeling runtime systems is validated through simulation. We illustrate the effectiveness of our model by comparing the performance of two existing workload adaptation algorithms.