An optimal value-based admission policy and its reflective use in real-time systems

This paper deals with planning system activities to support applications th at have different contrasting requirements including timing constraints on tasks execution and correctness requirements. Our approach is based on a si mple yet effective formulation of a value structure associated to the appli cation tasks. Values are associated to each relevant outcome thus accountin g for successful executions as well as for those which violate the applicat ion requirements. Moreover we assume degradable real time systems equipped with several execution techniques characterised by different execution cost s and different levels of fulfilment of requirements (and associated reward ). We propose an admission algorithm to select the part of the offered load to be executed, should overload occur. For all the admitted tasks the algo rithm selects also the most suitable execution technique (among those avail able) to optimise the expected cumulated reward. We show that the algorithm provides the best solution to the optimisation problem resorting to the li near programming theory. Then we discuss the applicability of this result t o systems operating in dynamic environments. A planner component is defined , responsible to collect information on the current status of the system an d of its environment. The planner decides when a new 'plan' is required, an d dynamically executes the admission algorithm to properly tune the usage o f system resources.