This paper focuses on the scheduling of tasks with hard and soft real-time constraints
in open and dynamic real-time systems. It starts by presenting a capacity
sharing and stealing (CSS) strategy that supports the coexistence of guaranteed
and non-guaranteed bandwidth servers to efficiently handle soft-tasks’ overloads by
making additional capacity available from two sources: (i) reclaiming unused reserved
capacity when jobs complete in less than their budgeted execution time and
(ii) stealing reserved capacity from inactive non-isolated servers used to schedule
best-effort jobs.
CSS is then combined with the concept of bandwidth inheritance to efficiently
exchange reserved bandwidth among sets of inter-dependent tasks which share resources
and exhibit precedence constraints, assuming no previous information on
critical sections and computation times is available. The proposed Capacity Exchange
Protocol (CXP) has a better performance and a lower overhead when compared
against other available solutions and introduces a novel approach to integrate
precedence constraints among tasks of open real-time systems
