Execution Overrun Management for Fixed-Priority Preemptive Scheduling of Sporadic Graph Tasks

In this paper, we consider a real-time application composed of graphs of subtasks. We present a mechanism for execution-overrun management in realtime systems. A subtask exceeding its prescribed execution duration can result in multiple failures (cascading effect). Yet, a task execution overrun does not necessarily lead to a deadline miss. Indeed, a system with enough free resources can self-stabilize without compromising the timeliness constraints of the subtasks in the system. We propose a mechanism based on the notion of allowance that enables to cope with execution overruns before a deadline miss. The task allowance depends on free resources. We show how to determine the maximum allowance duration a subtask can be allowed to proceed with it execution without compromising the real-time constraints of all the subtasks. We show how to determine the maximum allowance of a subtask from the feasibility conditions of sporadic graphs of subtasks scheduled with a preemptive fixed priority scheduling