Static Priority Scheduling Research Articles

Dynamic priority-based bandwidth allocation scheme for machine type communications

The burgeoning realm of Machine Type Communications (MTC) has ushered in a paradigm shift in wireless communication, necessitating innovative strategies to efficiently manage diverse application requirements. This paper presents a pioneering Dynamic Priority-based Bandwidth Allocation (DPBA) scheme tailored specifically for MTC scenarios, encompassing both MTC and Human Type Communications (HTC) coexistence. DPBA employs an adaptive framework addressing dynamic MTC traffic, optimizing resource use while meeting latency constraints and sporadic data patterns. By dynamically prioritizing MTC applications based on requirements, the scheme allocates bandwidth for reliable data delivery. DPBA extends to MTC and HTC coexistence, managing diverse quality demands. This underlines its versatility and capacity to serve distinct needs in a shared spectrum. To substantiate its performance, the DPBA scheme is rigorously evaluated against a spectrum of related allocation methods like Proportional Fairness (PF), Static Priority Scheduling (SPS), and the Machine Learning-based Scheme (MLS), DPBA excels in simulations, minimizing packet loss, latency, enhancing throughput and ensuring fairness, surpassing benchmarks. This research underscores the critical importance of tailored bandwidth allocation strategies in advancing MTC and HTC coexistent environments. With its adaptability, efficiency, and remarkable performance, the DPBA scheme emerges as a cornerstone in the trajectory of wireless communication networks, catering to the distinct requirements of both MTC and HTC applications.

RED-SP-CoDel: Random early detection with static priority scheduling and controlled delay AQM in programmable data planes

Emerging network application paradigms, such as the Tactile Internet, re-emphasize the need for different Quality of Service (QoS) levels. Due to the large packet buffers in the underlying network data plane, Active Queue Management (AQM) is generally required to curtail packet latencies for flows requiring high QoS levels. At the same time, programmable data planes, such as P4, enable packet processing at line-speed, albeit with limited packet processing functionalities. However, the existing AQM mechanisms that support QoS differentiation are too complex to readily run on P4, while the existing AQM mechanisms that run on P4 do generally not support effective QoS differentiation. We address this gap by developing to the best of our knowledge the first AQM mechanism that supports effective QoS differentiation while running on P4. Specifically, we propose SP-CoDel, which combines the well-known Controlled Delay (CoDel) AQM mechanism with Static Priority (SP) scheduling for QoS differentiation. Also, we propose RED-SP-CoDel, which adds a RED AQM component to SP-CoDel so as to make the AQM with priorities essentially parameterless. As a community resource contribution, we substantially extend the existing P4Simulator to the novel fused P4-NS3 Simulator so as to enable the evaluation of packet processing mechanisms through the combined functionalities of P4 device emulation and NS3 packet simulation. Evaluations conducted with the P4 reference switch model in the P4-NS3 Simulator indicate that SP-CoDel and RED-SP-CoDel provide high QoS to high-priority data streams, i.e., significantly reduce latency and packet loss compared to CoDel, while effectively mitigating bufferbloat.

An Integration of Open-Source Resources in Distance Teaching for Real-Time Embedded System Using Arduino Microcontroller and Freertos

Distance learning has become a crucial alternativein education system worldwide since the Covid-19 pandemic happened. An affordable and accessible solution is essentialto enable a quality remote teaching and learning experience for each student. Real-Time Embedded System (RTES) is about applying real-time system in an embedded system (e.g., microcontroller) in ways that both logical and temporal requirements are fulfilled. A special attention shall be on the temporal response analysis so that students can have a clear distinction between microcontrollers with and without real-time system.Since there is a lack of accessible traceable studies about how to utilize the open-source platform inintroducing the key RTES concepts, this study aims to evaluate the feasibility of an integration of open-source resources (i.e., SimSo simulator, Arduino platform and FreeRTOSAPI) in teaching RTES remotely and to provide real-time learning experience about RTES concepts without additional components or wiring out of school. First, each student was introduced to the ways to integrate existing open-source resources so that each of them could develop RTES in their placesusing a FreeRTOS compatible microcontroller.RTES concepts of task, hyperperiod, task scheduling, pre-emption,static-priority scheduling algorithms, and mutual exclusion in resource sharing were delivered using the proposed infrastructure. Results show that an obvious context switch could be observed when pre-emption happened. Finding indicates that the proposed integration was useful for students to understand the complex RTES concepts e.g., task scheduling, pre-emption, and mutuallyexclusion.Since positive responses were received from students in two consecutive semesters, the proposed infrastructure is an affordable and accessible distance learning alternative in assisting students to understand RTES concepts.

Queue assignment for fixed-priority real-time flows in time-sensitive networks: Hardness and algorithm

Abstract Time sensitive networks (TSNs) enable deterministic real-time communication over Ethernet networks. According to IEEE 802.1Qbv standards, TSN switches use gates between queues and their corresponding egress ports to facilitate timing-deterministic communications. Management of switch resources, such as queues, has a significant impact on the schedulability of real-time flows. In this paper, we look into the theoretical foundation of queue management in TSN switches. We prove that the queue assignment problem for real-time flows on time sensitive networks under static priority scheduling is NP-hard in the strong sense, even if the number of queues per port is 3. Then we formulate the problem as a satisfiability modulo theories (SMT) specification. Besides, we propose a worst case response time analysis and a fast heuristic algorithms by eliminating scheduling conflicts. Experiments with randomly generated workload demonstrate the effectiveness of our algorithms for queue assignment of real-time flows.

Hybrid Scheduler (S_LST) for Soft Real-Time System based on Static and Dynamic Algorithm

In the Soft Real-Time System scheduling process with the processor is a critical task. The system schedules the processes on a processor in a time interval, and hence the processes get chance to executes on the processor. Priority-driven scheduling algorithms are sub-categorized into mainly two categories called Static Priority and Dynamic Priority Scheduler. Critical Analysis of more static and dynamic priority scheduling algorithms have been discussed in this paper. This paper has covered the static priority algorithms like Rate Monotonic (RM) and Shortest Job First (SJF) and the dynamic priority algorithms like Earliest Deadline First (EDF) and Least Slack Time First (LST). These all algorithms have been analyzed with preemptive process set and this paper has considered all the process set are periodic. This paper has also proposed a hybrid approach for efficient scheduling. In a critical analysis, it has been observed that while scheduling in underload situation dynamic priority algorithms perform well and even EDF also make sure that all process will meet their deadline. However, in an overload situation, the performance of dynamic priority algorithms reduce quickly, and most of the task will miss its deadline, whereas static priority scheduling algorithms miss a few deadlines, even it is possible to schedule all processes in underload situation, whereas in an overload situation, the static algorithms perform well compared to the dynamic scheduler. This paper is proposing one Hybrid algorithm call S_LST which uses the concept of LST and SJF scheduling algorithm. This algorithm has been applied to the periodic task set, and observations are registered. We have observed the Success Ratio (SR) & Effective CPU Utilization (ECU) and compared all algorithms in the same conditions. It is noted that instead of using LST and SJF as an independent algorithm, Hybrid algorithm S_LST performs well in underload and overload scenario. Practical investigations have been led on a huge dataset. Data Set consists of the 7000+ process set, and each process set has one to nine processes and load varies between 0.5 to 5. It has been tried on 500-time unit to approve the rightness everything being equal.

Open Problem—Regarding Static Priority Scheduling for Many-Server Queues with Reneging

We study the many-server queue shown in Figure 1(a). Customers from class j ∈ {1, 2} arrive according to renewal processes having rate λj > 0 and request processing. There are N ∈ {1, 2,…} servers, each working at rate one. All servers are fully flexible; that is, every server can serve customers from both classes. Each customer has a randomly distributed patience time that may depend on the class and reneges (abandons the system without receiving service) if service does not begin before the patience time expires. The system incurs the penalty p1 > 0 when a class 1 customer reneges and the penalty p2 > 0 when a class 2 customer reneges. Upon arrival, each class j customer independently samples from the distribution determined by cumulative distribution function (cdf) [Formula: see text] having mean 1/θj < ∞ to find its patience time and from the distribution determined by cdf [Formula: see text] having mean 1/μj < ∞ to determine its service time (that is, the required processing time).

Schedulability Analysis of Graph-Based Real-Time Task Model with Precedence Constraints

The timing requirements of real-time systems can be guaranteed by well-designed scheduling policies. The analysis of such scheduling uses an abstract task model of the system to diagnose the practicability of timing requirements. The task models have evolved from periodic models to more sophisticated graph-based ones, among which digraph real-time (DRT) task model is the most applicable because of its good expressiveness and analysis efficiency. However, the DRT model cannot support the commonly used precedence constraints within or between tasks. In this paper, we propose a new task model that extends the DRT model to support precedence constraints. Based on our model, we present two methods of uniprocessor schedulability analysis for static priority scheduling policy and earliest deadline first (EDF) scheduling policy. We also introduce an optimization technique to improve the efficiency of model analysis. Our experiments show that, despite a high computational complexity of the problem, our approach scales very well for large sets of tasks with precedence constraints.

Mixed Harmonic Runnable Scheduling for Automotive Software on Multi-Core Processors

The performance of automotive electronic control units (ECUs) has improved following the development of multi-core processors. These processors facilitate fast computing performance without increasing clock speed. System developers partition automotive application runnables to have parallelizability and avoid interference between various software modules. To improve the performance of such systems, an efficient scheduler is necessary. In this regard, for multi-core ECUs, the automotive open system architecture (AUTOSAR) suggests partitioned static priority scheduling for parallelized software. In the AUTOSAR approach, clustering and partitioning of runnables for specific cores becomes difficult, but there is no exact criterion followed for partitioning the runnables. Consequently, cores are not balanced against loads, and under contingency conditions, there is a chance that tasks will miss deadlines. In this study, we address this problem by exploring a mixed harmonic runnable scheduling algorithm that includes partitioned scheduling. We tested this algorithm using high load conditions under contingency consequences, and we evaluated it using models of periodic runnables, periodic interrupts, and event-triggered interrupts. The performance parameters considered in this paper are balancing performance and the deadline missing rate. Our results indicate that the proposed algorithm can contribute toward improving the functional safety of vehicles.

Response time analysis of digraph real-time tasks scheduled with static priority: generalization, approximation, and improvement

Graph-based task models have been studied to better model and analyze the schedulability of real-time systems. Among them, the digraph task model, with its powerful expressiveness to describe the behavior of a large class of real-time tasks, receives a wide range of interests recently. However, the exact schedulability analysis of digraph tasks on a uni-processor with preemptive static-priority scheduling has been shown to be coNP-hard. Approximate analyses based on the request and interference bound functions (\(\textit{rbf}\) and \(\textit{ibf}\)) have been proposed to improve the analysis efficiency. In this work, we summarize the existing results on these analysis techniques, and seek to further improve their generality, complexity, and accuracy. Specifically, we develop analysis techniques for tasks with arbitrary deadlines. We prove the periodicity of interference bound function such that it can be expressed as a finite aperiodic part and an infinite periodic part, which makes the asymptotic complexity of its calculation independent from the length of the time interval. Moreover, we develop a linear upper bound on \(\textit{ibf}\) that is tighter than that of \(\textit{rbf}\), to derive a better response time bound.

A WEAKLY HARD SCHEDULING APPROACH OF PARTITIONED SCHEDULING ON MULTIPROCESSOR SYSTEMS

Real-time systems or tasks can be classified into three categories, based on the “seriousness” of deadline misses – hard, soft and weakly hard real-time tasks. The consequences of a deadline miss of a hard real-time task can be prohibitively expensive because all the tasks must meet their deadlines whereas soft real-time tasks tolerate “some” deadline misses. Meanwhile, in a weakly hard real-time task, the distribution of its met and missed deadlines is stated and specified precisely. As real-time application systems increasingly come to be implemented upon multiprocessor environments, thus, this study applies multiprocessor scheduling approach for verification of weakly hard real-time tasks and to guaranteeing the timing requirements of the tasks. In fact, within the multiprocessor, the task allocation problem seem even harder than in uniprocessor case; thus, in order to cater that problem, the sufficient and efficient scheduling algorithm supported by accurate schedulability analysis technique is present to provide weakly hard real-time guarantees. In this paper, a weakly hard scheduling approach has been proposed and schedulability analysis of proposed approach consists of the partitioned multiprocessor scheduling techniques with solutions for the bin-packing problem, called R-BOUND-MP-NFRNS (R-BOUND-MP with next-fit-ring noscaling) combining with the exact analysis, named hyperperiod analysis and deadline models; weakly hard constraints and µ-pattern under static priority scheduling. Then, Matlab simulation tool is used in order to validate the result of analysis. From the evaluation results, it can be proven that the proposed approach outperforms the existing approaches in terms of satisfaction of the tasks deadlines.

A Mixed Approach Scheduling Algorithm for Multicore Automotive ECUs at Contingency Conditions

Automotive ECUs have been upgraded with multicore processor implementation. It has the benefits of achieving high computing power without increasing the clock speed. System developers partition the automotive application tasks to have parallelizability and avoid interference between various software modules. Task intensive applications are assigned to multiple CPU cores. To improve the performance of such systems, there has to be an efficient task scheduler. In this regard, the Automotive Open System Architecture (AUTOSAR) suggests partitioned static priority scheduling for parallelized software for the multicore ECUs. In this approach, the difficulty lies with task clustering and partitioning for specific cores. There is no exact criterion to be followed to partition the tasks. Due to which cores are not balanced with loads. Under contingency conditions, there are chances of tasks missing deadlines. This paper addresses this issue by exploring a mixed approach scheduling algorithm which has features of both static and dynamic scheduling and also few adaptations of partitioned and global scheduling. With this algorithm, high load conditions under contingency consequences are tested. This algorithm was run and tested using a scheduling simulator with real time task models of periodic tasks, angle synchronous interrupts and event triggered interrupts. The performance parameters considered here are, the % of core utilization, response time, deadlines missing rate. It has been verified that, this proposed algorithm is able to find a feasible schedule under various contingency scenarios and contributes to improve the safety level of the vehicle.

Priority-Driven Swapping-Based Scheduling of Aperiodic Real-Time Messages Over EtherCAT Networks

Real-time Ethernet (RTE) technologies are becoming increasingly popular, as they provide high bandwidth and are able to meet the requirements of industrial real-time communications. Among RTE protocols, the EtherCAT standard is suitable for motion control and closed-loop control applications, which require very short cycle times. As EtherCAT was specifically devised for periodic traffic, aperiodic real-time transmissions are far from being efficient, as they entail long cycle times. To overcome this limitation, this paper presents a general framework for priority-driven swapping (PdS)-based scheduling of aperiodic real-time messages over EtherCAT networks, which uniformly covers both dynamic and static priority and allows for very short cycle times. This paper provides a description of the PdS framework, a schedulability analysis for both static priority and dynamic priority scheduling, and simulative assessments obtained through OMNeT++ simulations.

Truthful Mechanisms for Allocating a Single Processor to Sporadic Tasks in Competitive Real-Time Environments

In a non-competitive environment, sporadic real-time task scheduling on a single processor is well understood. In this paper, we consider a competitive environment comprising several real-time tasks vying for execution upon a shared single processor. Each task obtains a value if the processor successfully schedules all its jobs. Our objective is to select a feasible subset of these tasks to maximize the sum of values of selected tasks. We consider both dynamic-priority and static-priority scheduling algorithms. There are algorithms for solving these problems in non-competitive settings. However, we consider these problems in an economic setting in which each task is owned by a selfish agent. Each agent reports the characteristics of her own task to the processor owner. The processor owner uses a mechanism to allocate the processor to a subset of agents and to determine the payment of each agent. Since agents are selfish, they may try to manipulate the mechanism to obtain the processor. We are interested in truthful mechanisms in which it is always in agents’ best interest to report the true characteristics of their tasks. We design exact and approximate truthful mechanisms for this competitive environment and study their performance.

Applying dynamic priority scheduling scheme to static systems of pinwheel task model in power-aware scheduling.

Power-aware scheduling reduces CPU energy consumption in hard real-time systems through dynamic voltage scaling (DVS). In this paper, we deal with pinwheel task model which is known as static and predictable task model and could be applied to various embedded or ubiquitous systems. In pinwheel task model, each task's priority is static and its execution sequence could be predetermined. There have been many static approaches to power-aware scheduling in pinwheel task model. But, in this paper, we will show that the dynamic priority scheduling results in power-aware scheduling could be applied to pinwheel task model. This method is more effective than adopting the previous static priority scheduling methods in saving energy consumption and, for the system being still static, it is more tractable and applicable to small sized embedded or ubiquitous computing. Also, we introduce a novel power-aware scheduling algorithm which exploits all slacks under preemptive earliest-deadline first scheduling which is optimal in uniprocessor system. The dynamic priority method presented in this paper could be applied directly to static systems of pinwheel task model. The simulation results show that the proposed algorithm with the algorithmic complexity of O(n) reduces the energy consumption by 10–80% over the existing algorithms.

Reliability analysis of real-time fault-tolerant task models

One notable advantage of Model-Driven Architecture (MDA) method is that software developers could do sufficient analysis and tests on software models in the design phase, which helps construct high confidence on the expected software behaviors and performance, especially for safety-critical real-time software. Most existing literature of reliability analysis ignores the effects from those deadline requirements of tasks which are critical properties for real-time software and thus cannot be ignored. Considering the contradictory relationship between the deadline requirements and time costs of fault tolerance in real-time tasks, in this paper, we present a novel reliability model, which takes schedulability as one of the major factors affecting the reliability, to analyze reliability of the task execution model in real-time software design phase. The tasks in this reliability model has no restrictions on their distributions and thus could be distributed on a multiprocessor or on a distributed system. Furthermore, the tasks also define arrival rates of faults and fault-tolerant mechanisms to model the occurrences of non-permanent faults and the corresponding time costs of fault handling. By analyzing the probability of tasks still being schedulable in the worst-case execution scenario with faults occurring, reliability and schedulability are combined into an unified analysis framework, and two algorithms for reliability analysis are given. To make this reliability model more pragmatic, we also present an estimation technique for estimating the fault arrival rate of each task. We show through two case studies respectively the detailed derivation process under static-priority scheduling in a multiprocessor system and in the design process of avionics software, and then analyze the factors affecting the reliability analysis by setting up simulation experiments. When no assumptions of fault occurrences made on the task model, this reliability model regresses to a generic schedulability model.

Handling Priorities in Optical Buffers

In this letter we focus on the construction of optical buffers exploiting a static priority scheduling policy. Optical Switches and fiber Delay Lines (SDLs) are used to build the proposed multiple input/output ports Optical Priority Multiplexers and Priority Switching Nodes, used for contention-resolution in Optical Packet Switched networks.

Deterministic end-to-end delay analysis in an avionics network

Avionics Full DupleX Switched Ethernet is a deterministic communication protocol for distributed embedded real-time applications over asynchronous channels. It is a promising technique that can replace the existing avionics data buses, such as ARINC429 and MIL-STD-1553B. One of the key challenges for deploying and maintaining Avionics Full DupleX Switched Ethernet is to determine the end-to-end transmission delay in such a network. This article aims at handling this challenge effectively applying a completely theoretical analysis. An analytical method based on the network calculus theory is presented in detail to calculate the end-to-end transmission delay in an Avionics Full DupleX Switched Ethernet network, which consists of many interconnect nodes with different scheduling disciplines. Further, this approach is improved by taking into account the effects of source node initial jitter and first in, first out optimization. Additionally, a Matlab/TrueTime simulation platform is constructed to verify the effectiveness of the method. Simulation results show that switches with advanced scheduling algorithms, i.e. static priority scheduling, can significantly improve the delay performance in a multi-hop network.

A Model to Partly but Reliably Distinguish DDOS Flood Traffic from Aggregated One

Reliable distinguishing DDOS flood traffic from aggregated traffic is desperately desired by reliable prevention of DDOS attacks. By reliable distinguishing, we mean that flood traffic can be distinguished from aggregated one for a predetermined probability. The basis to reliably distinguish flood traffic from aggregated one is reliable detection of signs of DDOS flood attacks. As is known, reliably distinguishing DDOS flood traffic from aggregated traffic becomes a tough task mainly due to the effects of flash‐crowd traffic. For this reason, this paper studies reliable detection in the underlying DiffServ network to use static‐priority schedulers. In this network environment, we present a method for reliable detection of signs of DDOS flood attacks for a given class with a given priority. There are two assumptions introduced in this study. One is that flash‐crowd traffic does not have all priorities but some. The other is that attack traffic has all priorities in all classes, otherwise an attacker cannot completely achieve its DDOS goal. Further, we suppose that the protected site is equipped with a sensor that has a signature library of the legitimate traffic with the priorities flash‐crowd traffic does not have. Based on those, we are able to reliably distinguish attack traffic from aggregated traffic with the priorities that flash‐crowd traffic does not have according to a given detection probability.

Analysis of discrete-time queueing systems with priority jumps

This text is a summary of the author’s PhD thesis supervised by Herwig Bruneel and Joris Walraevens, and defended on 5 March 2009 at Ghent University. The thesis is written in English and is available from the author upon request. The work deals with several priority scheduling disciplines with so-called priority jumps. An efficient priority scheduling discipline is of great importance in modern telecommunication devices. Static priority scheduling achieves maximum service differentiation between different types of traffic, but may have a too severe impact on the performance of lower-priority traffic. Introducing priority jumps aims for a more gradual service differentiation. In the thesis, we propose several (types of) jumping mechanisms, and we analyse their effect on the performance of a discrete-time queueing system.

An LP-Based Algorithm for Scheduling Preemptive and/or Non-Preemptive Real-Time Tasks

We consider a real-time system that requires the time stimuli to the system are processed through sequences of tasks to be within specified upper bounds, where the set of tasks can be the mixture of preemptive and non-preemptive tasks, and we propose an algorithm to design a static priority scheduling for the system. In the algorithm, local search is used to determine priorities of tasks, and whenever the priorities are fixed, the periods of tasks are determined. This subproblem can be described as a mathematical programming formulation and is solved via linear programming techniques. Finally, we report computational results for sample instances from a company.