Two-Level Iterative Queuing Modeling of Software Contention

Being able to model contention for software resources (e.g., a critical section or database lock) is paramount to building performance models that capture all aspects of the delay encountered by a process as it executes. Several methods have been offered for dealing with software contention and with message blocking in client-server systems. This paper presents a general, straightforward, easy to understand and implement, approach to modeling software contention using queuing networks. The approach, called SQNHQN, consists of a two-level iterative process. Two queuing networks are considered: one represents software resources (SQN) and the other hardware resources (HQN). Multiclass models are allowed and any solution technique—exact or approximate—can be used at any of the levels. This technique falls in the general category of fixed-point approximate models and is similar in nature to other approaches. The main difference lies in its simplicity. The process converges very fast in the examples examined. The results were validated against global balance equation solutions and are very accurate.