Research On Smooth Insertion Of Real-Time New Tasks

In a single processor real-time system,the overload caused by task acceleration or new task insertion can be solved by compression of the current task,which is called the bandwidth transfer in elastic scheduling.However,in order to avoid the loss of deadline while inserting new tasks,it is necessary to adopt the smooth insertion method,and the key of the smooth insertion problem is to find the earliest smooth-time.There is a preliminary method to find the earliest smooth time,called Simple way,the core of which is testing the smooth insertion point by gradually delay.This paper presents a more advanced result than the Simple way through literature research and simulation experiments.Firstly,based on EDF(Earliest Deadline First)algorithm,this paper describes the model of real-time periodic tasks as a triple that composed by execution time,initial period and compressed period in the case of multitask bandwidth transferring,and then again describes the bandwidth transfer of real-time multitasks and the transient process in elastic scheduling.Then the compression process of the current task and the calculation of processor requirements are analyzed in detail.Next,a Delay judgment criterion is put forward.In the process of proving the criterion,this paper points out that there are only two cases of deadline loss caused by the insertion of new tasks,the first is the deadline loss of current tasks,the second is that of new tasks,and the criterion is proved in both cases.The correctness of the Delay judgment criterion means that if a deadline d_x is lost due to releasing a new task at the current time,then at least?units should be delayed in the next round to ensure the satisfaction of d_x,where?is the check value generated in the previous round of attempts.In the last part,this paper constructs a new algorithm based on the Delay judgment criterion,named as Smart way,it can effectively improve the speed of calculation of the earliest smooth time.A good property of Smart way has been proved,which is helpful to further reduce the number of inspection rounds in the delay process.Then Smart way is verified and explained through the simulation example on real-time scheduling platform,and its efficiency is compared with Simple way,the comparison shows that the farther the smooth point is,the higher the efficiency of Smart way is.Delay judgment criteria and Smart way algorithm are new achievements in the research field of flexible scheduling.They are not only expected to provide some inspiration and thinking for scholars that interested in bandwidth transfer and other issues,but also to provide a theoretical framework for real-time application practice with corresponding needs.