  A model has been proposed in [Baruah et al., in Proceedings of the IEEE
Real-Time Systems Symposium 2012] for representing recurrent
precedence-constrained tasks to be executed on multiprocessor platforms, where
each recurrent task is modeled by a directed acyclic graph (DAG), a period, and
a relative deadline. Each vertex of the DAG represents a sequential job, while
the edges of the DAG represent precedence constraints between these jobs. All
the jobs of the DAG are released simultaneously and have to be completed within
some specified relative deadline. The task may release jobs in this manner an
unbounded number of times, with successive releases occurring at least the
specified period apart. The feasibility problem is to determine whether such a
recurrent task can be scheduled to always meet all deadlines on a specified
number of dedicated processors.
  The case of a single task has been considered in [Baruah et al., 2012]. The
main contribution of this paper is to consider the case of multiple tasks. We
show that EDF has a speedup bound of 2-1/m, where m is the number of
processors. Moreover, we present polynomial and pseudopolynomial schedulability
tests, of differing effectiveness, for determining whether a set of sporadic
DAG tasks can be scheduled by EDF to meet all deadlines on a specified number
of processors.
