336 research outputs found
Practical Schedulability Analysis for Generalized Sporadic Tasks in Distributed Real-Time Systems
Existing off-line schedulability analysis for real-time systems can only handle periodic or sporadic tasks with known minimum inter-arrival times. Modeling sporadic tasks with fixed minimum inter-arrival times is a poor approximation for systems in which tasks arrive in bursts, but have longer intervals between the bursts. In such cases, schedulability analysis based on the existing sporadic task model is pessimistic and seriously overestimates the task\u27s time demand. In this paper, we propose a generalized sporadic task model that characterizes arrival times more precisely than the traditional sporadic task model, and we develop a corresponding schedulability analysis that computes tighter bounds on worst-case response times. Experimental results show that when arrival time jitter increases, the new analysis more effectively guarantees schedulability of sporadic tasks
A Practical Schedulability Analysis for Generalized Sporadic Tasks in Distributed Real-Time Systems
Existing off-line schedulability analysis for real-time systems can only handle periodic or sporadic tasks with known minimum inter-arrival times. Modeling sporadic tasks with fixed minimum inter-arrival times is a poor approximation for systems in which tasks arrive in bursts, but have longer intervals between the bursts. In such cases, schedulability analysis based on the existing sporadic task model is pessimistic and seriously overestimates the task\u27s time demand. In this paper, we propose a generalized sporadic task model that characterizes arrival times more precisely than the traditional sporadic task model, and we develop a corresponding schedulability analysis that computes tighter bounds on worst-case response times. Experimental results show that when arrival time jitter increases, the new analysis more effectively guarantees schedulability of sporadic tasks
Reservation-Based Federated Scheduling for Parallel Real-Time Tasks
This paper considers the scheduling of parallel real-time tasks with
arbitrary-deadlines. Each job of a parallel task is described as a directed
acyclic graph (DAG). In contrast to prior work in this area, where
decomposition-based scheduling algorithms are proposed based on the
DAG-structure and inter-task interference is analyzed as self-suspending
behavior, this paper generalizes the federated scheduling approach. We propose
a reservation-based algorithm, called reservation-based federated scheduling,
that dominates federated scheduling. We provide general constraints for the
design of such systems and prove that reservation-based federated scheduling
has a constant speedup factor with respect to any optimal DAG task scheduler.
Furthermore, the presented algorithm can be used in conjunction with any
scheduler and scheduling analysis suitable for ordinary arbitrary-deadline
sporadic task sets, i.e., without parallelism
Utilization-Based Scheduling of Flexible Mixed-Criticality Real-Time Tasks
Mixed-criticality models are an emerging paradigm for the design of real-time
systems because of their significantly improved resource efficiency. However,
formal mixed-criticality models have traditionally been characterized by two
impractical assumptions: once \textit{any} high-criticality task overruns,
\textit{all} low-criticality tasks are suspended and \textit{all other}
high-criticality tasks are assumed to exhibit high-criticality behaviors at the
same time. In this paper, we propose a more realistic mixed-criticality model,
called the flexible mixed-criticality (FMC) model, in which these two issues
are addressed in a combined manner. In this new model, only the overrun task
itself is assumed to exhibit high-criticality behavior, while other
high-criticality tasks remain in the same mode as before. The guaranteed
service levels of low-criticality tasks are gracefully degraded with the
overruns of high-criticality tasks. We derive a utilization-based technique to
analyze the schedulability of this new mixed-criticality model under EDF-VD
scheduling. During runtime, the proposed test condition serves an important
criterion for dynamic service level tuning, by means of which the maximum
available execution budget for low-criticality tasks can be directly determined
with minimal overhead while guaranteeing mixed-criticality schedulability.
Experiments demonstrate the effectiveness of the FMC scheme compared with
state-of-the-art techniques.Comment: This paper has been submitted to IEEE Transaction on Computers (TC)
on Sept-09th-201
A static scheduling approach to enable safety-critical OpenMP applications
Parallel computation is fundamental to satisfy the performance requirements of advanced safety-critical systems. OpenMP is a good candidate to exploit the performance opportunities of parallel platforms. However, safety-critical systems are often based on static allocation strategies, whereas current OpenMP implementations are based on dynamic schedulers. This paper proposes two OpenMP-compliant static allocation approaches: an optimal but costly approach based on an ILP formulation, and a sub-optimal but tractable approach that computes a worst-case makespan bound close to the optimal one.This work is funded by the EU projects P-SOCRATES (FP7-ICT-2013-10) and HERCULES (H2020/ICT/2015/688860), and the Spanish Ministry of Science and Innovation under contract TIN2015-65316-P.Peer ReviewedPostprint (author's final draft
A Real-time Calculus Approach for Integrating Sporadic Events in Time-triggered Systems
In time-triggered systems, where the schedule table is predefined and
statically configured at design time, sporadic event-triggered (ET) tasks can
only be handled within specially dedicated slots or when time-triggered (TT)
tasks finish their execution early. We introduce a new paradigm for
synthesizing TT schedules that guarantee the correct temporal behavior of TT
tasks and the schedulability of sporadic ET tasks with arbitrary deadlines. The
approach first expresses a constraint for the TT task schedule in the form of a
maximal affine envelope that guarantees that as long as the schedule generation
respects this envelope, all sporadic ET tasks meet their deadline. The second
step consists of modeling this envelope as a burst limiting constraint and
building the TT schedule via simulating a modified Least-Laxity-First (LLF)
scheduler. Using this novel technique, we show that we achieve equal or better
schedulability and a faster schedule generation for most use-cases compared to
other approaches inspired by, e.g., hierarchical scheduling. Moreover, we
present an extension to our method that finds the most favourable schedule for
TT tasks with respect to ET schedulability, thus increasing the probability of
the computed TT schedule remaining feasible when ET tasks are later added or
changed
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