Performance analysis of dynamic priority shifting

We investigate the benefit of priority shifting for resource allocation in systems with a shared resource, where higher priority implies better service. Priority schemes where priority levels are assigned fixed shares of the resource experience underutilisation if there are only low-priority tasks present. In these situations, lower priority tasks can be ‘shifted up’ to higher priority. This increases overall system utilisation and improves the service experienced by low-priority tasks. We present a shifting framework, study its properties and develop a Petri net model for a shifting algorithm. We analyse the model in order to identify situations where shifting of priorities is beneficial