1 research outputs found
Sharp utilization thresholds for some real-time scheduling problems
Scheduling policies for real-time systems exhibit threshold behavior that is
related to the utilization of the task set they schedule, and in some cases
this threshold is sharp. For the rate monotonic scheduling policy, we show that
periodic workload with utilization less than a threshold can be
scheduled almost surely and that all workload with utilization greater than
is almost surely not schedulable. We study such sharp threshold
behavior in the context of processor scheduling using static task priorities,
not only for periodic real-time tasks but for aperiodic real-time tasks as
well. The notion of a utilization threshold provides a simple schedulability
test for most real-time applications. These results improve our understanding
of scheduling policies and provide an interesting characterization of the
typical behavior of policies. The threshold is sharp (small deviations around
the threshold cause schedulability, as a property, to appear or disappear) for
most policies; this is a happy consequence that can be used to address the
limitations of existing utilization-based tests for schedulability. We
demonstrate the use of such an approach for balancing power consumption with
the need to meet deadlines in web servers