Choice of aggregation groups for layered performance model simplification

The authors1 previously showed that a complex layered performance model could be simplified by aggregating the contributions of subsystems, following a few simple principles which give good accuracy in many cases. The question of which subsystems to merge in layered performance models is further examined here, leading to identifying groups of subsystems (corresponding to "tasks" in layered queuing models) which can be safely aggregated. The grouping begins by identifying tasks which should be preserved, not aggregated, including those which are (or might become) bottlenecks. Then the groups are defined by their relationship to these preserved tasks. Aggregation by groups provides adequate accuracy in the vast majority of cases examined