3 research outputs found
Push Forward: Global Fixed-Priority Scheduling of Arbitrary-Deadline Sporadic Task Systems
The sporadic task model is often used to analyze recurrent execution of
identical tasks in real-time systems. A sporadic task defines an infinite
sequence of task instances, also called jobs, that arrive under the minimum
inter-arrival time constraint. To ensure the system safety, timeliness has to
be guaranteed in addition to functional correctness, i.e., all jobs of all
tasks have to be finished before the job deadlines. We focus on analyzing
arbitrary-deadline task sets on a homogeneous (identical) multiprocessor system
under any given global fixed-priority scheduling approach and provide a series
of schedulability tests with different tradeoffs between their time complexity
and their accuracy. Under the arbitrary-deadline setting, the relative deadline
of a task can be longer than the minimum inter-arrival time of the jobs of the
task. We show that global deadline-monotonic (DM) scheduling has a speedup
bound of against any optimal scheduling algorithms, where is the
number of identical processors, and prove that this bound is asymptotically
tight
k2Q: A Quadratic-Form Response Time and Schedulability Analysis Framework for Utilization-Based Analysis
In this paper, we present a general response-time analysis and
schedulability-test framework, called k2Q (k to Q). It provides automatic
constructions of closed-form quadratic bounds or utilization bounds for a wide
range of applications in real-time systems under fixed-priority scheduling. The
key of the framework is a -point schedulability test or a -point response
time analysis that is based on the utilizations and the execution times of
higher-priority tasks. The natural condition of k2Q is a quadratic form
for testing the schedulability or analyzing the response time. The response
time analysis and the schedulability analysis provided by the framework can be
viewed as a "blackbox" interface that can result in sufficient
utilization-based analysis. Since the framework is independent from the task
and platform models, it can be applied to a wide range of applications.
We show the generality of k2Q by applying it to several different task
models. k2Q produces better uniprocessor and/or multiprocessor schedulability
tests not only for the traditional sporadic task model, but also more
expressive task models such as the generalized multi-frame task model and the
acyclic task model. Another interesting contribution is that in the past,
exponential-time schedulability tests were typically not recommended and most
of time ignored due to high complexity. We have successfully shown that
exponential-time schedulability tests may lead to good polynomial-time tests
(almost automatically) by using the k2Q framework.Comment: arXiv admin note: substantial text overlap with arXiv:1505.02155;
text overlap with arXiv:1501.07084, a complete version of RTSS 201
Exact Polynomial Time Algorithm for the Response Time Analysis of Harmonic Tasks with Constrained Release Jitter
In some important application areas of hard real-time systems, preemptive
sporadic tasks with harmonic periods and constraint deadlines running upon a
uni-processor platform play an important role. We propose a new algorithm for
determining the exact worst-case response time for a task that has a lower
computational complexity (linear in the number of tasks) than the known
algorithm developed for the same system class. We also allow the task
executions to start delayed due to release jitter if they are within certain
value ranges. For checking if these constraints are met we define a constraint
programming problem that has a special structure and can be solved with
heuristic components in a time that is linear in the task number. If the check
determines the admissibility of the jitter values, the linear time algorithm
can be used to determine the worst-case response time also for jitter-aware
systems