Three traditional performance modeling techniques are analytic modeling, simulation, and measurement. Pure analytic modeling is based on a theoretical operation count of an algorithm and its operation and the establishment of algebraic timing formulas, but accuracy can be low. Simulation techniques are expensive and also have problems with accuracy.
Measurement alone is limited in generality.
Our approach is to use measurement based analytic modeling with algebraic timing formulae based on theoretical time dependencies and free parameters in the model, but with measurements used to calibrate the parameters. The scalability of a parallel system or code is a measure of its ability to utilize increasing processing resources.