Scheduling periodic tasks in a hard real-time environment

We consider a real-time scheduling problem that occurs in the design of software-based aircraft control. The goal is to distribute tasks $au_i=(c_i,p_i)$ on a minimum number of identical machines and to compute offsets $a_i$ for the tasks such that no collision occurs. A task $au_i$ releases a job of running time $c_i$ at each time $a_i + kcdot p_i,k in mathbb{N}_0$ and a collision occurs if two jobs are simultaneously active on the same machine. We shed some light on the complexity and approximability landscape of this problem. Although the problem cannot be approximated within a factor of $n^{1-varepsilon}$ for any $varepsilon>0$, an interesting restriction is much more tractable: If the periods are dividing (for each $i,j$ one has $p_i | p_j$ or $p_j | p_i$), the problem allows for a better structured representation of solutions, which leads to a 2-approximation. This result is tight, even asymptotically

On Scheduling Real-Time Periodic Tasks in a Multiprocessor Environment.

Real-Time periodic tasks are at the heart of many critical processing computer systems. Nuclear power plants, military command and control systems, aircraft automatic flight control systems, hospital life-support equipment all require precise processing performed within very strict timelines. Missing deadlines can have catastrophic consequences. The rate-monotonic priority assignment policy for scheduling hard-deadline periodic tasks was developed to guarantee those deadlines. In this thesis, we study the problem of scheduling hard-deadline periodic tasks. We begin by surveying the current state of multiprocessor rate-monotonic scheduling and reviewing earlier work. We present the results of a number of experiments we conducted to evaluate the performance of several scheduling heuristics. These heuristics assumed a homogeneous multiprocessing environment. We relax that restriction and introduce three allocation heuristics for scheduling tasks on heterogeneous multiprocessors. Furthermore, we analyze the performance of the proposed algorithms. We compare the quality of the solutions produced by these algorithms and measure them against the optimal solution. Lacking in the current set of real-time multiprocessor heuristics is the awareness of communication between tasks. We add communication into the scheduling model and provide an algorithm to minimize the amount of data transfer between tasks. Furthermore, we examine the performance of this heuristic and compare the schedules it produces with optimal solutions. Lastly, we introduce a scheduling and analysis fool that incorporates several scheduling heuristics. New heuristics are easily added to the tool. The goal of the tool is to help system designers/developers study the performance of different heuristics in scheduling real-time periodic tasks. The tool helps answer “what if” questions, which may also help designers tune their systems to achieve better performance while meeting deadlines

An efficient aperiodic task server for energy harvesting embedded systems

International audienceThe energy existing in our environment can be converted into electricity to supply a wireless device such as sensor node. In this paper, we will address a problem of scheduling for a device that executes a mixed set of real-time tasks, composed of aperiodic and hard deadline periodic tasks. High responsiveness of the aperiodic tasks and timeliness of the periodic tasks can be performed through an aperiodic task server that takes into account both time and energy limitations. This paper describes an extension of the well known TBS (Total Bandwidth Server) which is energy harvesting aware. The performance of the new aperiodic server, called TB-H, is evaluated and compared to background approaches through simulation experiments

Feasibility Test Verification Method For Nonsymmetric Release Time Task Scheduling

This paper discusses problems associated with scheduling periodic task on a uniprocessor in a hard, real-time processing environment using a static-priority, preemptive-resume operating system. Task sets containing a single periodic task with two Ned release periocis of unequal length are examined. Ihe nonsymmetric scheduling algorithm is based on the rate monotonic scheduling algorithm which assigns higher task priorities to tasks with shorter release periods. me effects on processor utilization using two dirkrent priority assignment schemes are examined; one with task priorities sorted by the average release periods and the other with priorities sorted using the short nonsymmetric task period with the average period lengths for the remaining task. Results indicate that the second scheme had higher breakdown utilizations than the first one, and that the second scheme, for task sets with a low utilization nonsymmetric task, results in little or no loss in the overall task set utilization

Flexible Scheduling in Multimedia Kernels: an Overview

Current Hard Real-Time (HRT) kernels have their timely behaviour guaranteed on the cost of a rather restrictive use of the available resources. This makes current HRT scheduling techniques inadequate for use in a multimedia environment where we can make a considerable profit by a better and more flexible use of the resources. We will show that we can improve the flexibility and efficiency of multimedia kernels. Therefore we introduce Real Time Transactions (RTT) with Deadline Inheritance policies for a small class of scheduling algorithms and we will evaluate these algorithms for use in a multimedia environmen

Securing Real-Time Internet-of-Things

Modern embedded and cyber-physical systems are ubiquitous. A large number of critical cyber-physical systems have real-time requirements (e.g., avionics, automobiles, power grids, manufacturing systems, industrial control systems, etc.). Recent developments and new functionality requires real-time embedded devices to be connected to the Internet. This gives rise to the real-time Internet-of-things (RT-IoT) that promises a better user experience through stronger connectivity and efficient use of next-generation embedded devices. However RT- IoT are also increasingly becoming targets for cyber-attacks which is exacerbated by this increased connectivity. This paper gives an introduction to RT-IoT systems, an outlook of current approaches and possible research challenges towards secure RT- IoT frameworks