1. A computer-implemented method of evaluating a performance of a computer system based on a queueing model, comprising: defining a workload comprising a plurality of service requests, each service request corresponding to a class of a plurality of classes; applying, by one or more processors, the workload to the computer system that receives and processes the plurality of service requests; measuring, by the one or more processors, a response time of the computer system for each request of the workload to provide a plurality of measured response times; determining, by the one or more processors, a mean response time for each class based on the plurality of measured response times; estimating, by the one or more processors, a mean service demand for each class based on the mean response time for a respective class and a base queueing model that represents the computer system to provide a plurality of mean service demands, each of the plurality of mean service demands defining an average time a respective service request is attended to by the computer system; generating, by the one or more processors, the queueing model based on the mean service demands and characteristics of the workload, the queueing model modeling queuing of the plurality of service requests submitted to the computer system; and processing the queueing model using a plurality of inputs to evaluate the performance of the computer system.