A method for modeling performance of an information technology system having one or more servers for serving a number of types of transactions includes modeling a service time of each transaction type at each server and a processor overhead at each server as one of a polynomial, exponential, or logarithmic function of the average arrival rate of each transaction type at the corresponding server to generate service time and processor overhead functions and inferring optimal values of coefficients in the service time and processor overhead functions to generate a performance model of the information technology system.