scholarly journals Performance Assessment of Linux Kernels with PREEMPT_RT on ARM-Based Embedded Devices

Electronics ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1331
Author(s):  
George K. Adam ◽  
Nikos Petrellis ◽  
Lambros T. Doulos
Keyword(s):  
Real Time ◽  
Performance Metrics ◽  
Evaluation Methodology ◽  
Performance Measurements ◽  
Periodic Tasks ◽  
Embedded Devices ◽  
Worst Case ◽  
Time Performance ◽  
Software Modules ◽  
Response Task

This work investigates the real-time performance of Linux kernels and distributions with a PREEMPT_RT real-time patch on ARM-based embedded devices. Experimental measurements, which are mainly based on heuristic methods, provide novel insights into Linux real-time performance on ARM-based embedded devices (e.g., BeagleBoard and RaspberryPi). Evaluations of the Linux real-time performance are based on specific real-time software measurement modules, developed for this purpose, and the use of a standard benchmark tool, cyclictest. Software modules were designed upon the introduction of a new response task model, an innovative aspect of this work. Measurements include the latency of response tasks at user and kernel space, the response on the execution of periodic tasks, the maximum sustained frequency and general latency performance metrics. The results show that in such systems the PREEMPT_RT patch provides more improved real-time performance than the default Linux kernels. The latencies and particularly the worst-case latencies are reduced with real-time support, thus making such devices running Linux with PREEMPT_RT more appropriate for use in time-sensitive embedded control systems and applications. Furthermore, the proposed performance measurements approach and evaluation methodology could be applied and deployed on other Linux-based real-time platforms.

scholarly journals Real-Time Performance and Response Latency Measurements of Linux Kernels on Single-Board Computers

Computers ◽  
2021 ◽  
Vol 10 (5) ◽  
pp. 64
Author(s):  
George K. Adam
Keyword(s):  
Real Time ◽  
Safety Margin ◽  
Evaluation Methodology ◽  
Raspberry Pi ◽  
Performance Measurements ◽  
Worst Case ◽  
Time Performance ◽  
Software Modules ◽  
Real Time Applications ◽  
Embedded Development

This research performs real-time measurements of Linux kernels with real-time support provided by the PREEMPT_RT patch on embedded development devices such as BeagleBoard and Raspberry Pi. The experimental measurements of the Linux real-time performance on these devices are based on real-time software modules developed specifically for the purposes of this research. Taking in consideration the constraints of the specific hardware platforms under investigation, new measurements software was developed. The measurement algorithms are designed upon response and periodic task models. Measurements investigate latencies of real-time applications at user and kernel space. An outcome of this research is that the proposed performance measurements approach and evaluation methodology could be applied and deployed on other Linux-based boards and platforms. Furthermore, the results demonstrate that the PREEMPT_RT patch overall improves the Linux kernel real-time performance compared to the standard one. The reduced worst-case latencies on such devices running Linux with real-time support could make them potentially more suitable for real-time applications as long as a latency value of about 160 μs, as an upper bound, is an acceptable safety margin.

scholarly journals Hierarchical Scheduling for Real-Time Periodic Tasks in Symmetric Multiprocessing

2021 ◽  
Author(s):  
Tom Springer ◽  
Peiyi Zhao
Keyword(s):  
Real Time ◽  
Response Times ◽  
Periodic Tasks ◽  
Global Scheduling ◽  
Hierarchical Scheduling ◽  
Time Performance ◽  
Performance Guarantees ◽  
Partitioned Scheduling ◽  
Hard Real Time ◽  
Time Periodic

In this paper, we present a new hierarchical scheduling framework for periodic tasks in symmetric multiprocessor (SMP) platforms. Partitioned and global scheduling are the two main approaches used by SMP based systems where global scheduling is recommended for overall performance and partitioned scheduling is recommended for hard real-time performance. Our approach combines both the global and partitioned approaches of traditional SMP-based schedulers to provide hard real-time performance guarantees for critical tasks and improved response times for soft real-time tasks. Implemented as part of VxWorks, the results are confirmed using a real-time benchmark application, where response times were improved for soft real-time tasks while still providing hard real-time performance.

Development of real-time performance metrics for manually-guided spacecraft operations

2016 ◽  
Author(s):  
John A. Karasinski ◽  
Stephen K. Robinson ◽  
Kevin R. Duda ◽  
Zahar Prasov
Keyword(s):  
Real Time ◽  
Performance Metrics ◽  
Time Performance

scholarly journals Binocular intelligent following robot based on YOLO-LITE

2021 ◽  
Vol 336 ◽  
pp. 03002
Author(s):  
Yuanyuan Zheng ◽  
Jun Ge
Keyword(s):  
Neural Network ◽  
Real Time ◽  
Deep Neural Network ◽  
Frame Rate ◽  
Raspberry Pi ◽  
Detection Accuracy ◽  
Location Error ◽  
Embedded Devices ◽  
Robot System ◽  
Time Performance

In order to solve the problem that the deep neural network model is large in scale, the calculation time is too long, and the real-time performance is severely limited when combined with embedded devices, so studied the intelligent follower robot system based on YOLO-LITE algorithm combined with Raspberry Pi 3B+. The system mainly includes camera processing, target detection and other modules. Obtained the internal and external parameters of the camera through calibration, and according to these parameters to correct the binocular camera. Recognized and located the target in each frame of image, calculated the distance from the camera to the target and the center location error, and driven the car to move. The experimental results show that the following car has excellent real-time performance, the average detection frame rate can reach 20Fps, and the average detection accuracy can reach more than 80%.

New Optimal Preemptively Scheduling for Real-Time Reconfigurable Sporadic Tasks Based on Earliest Deadline First Algorithm

2012 ◽  
Vol 4 (2) ◽  
pp. 65-81 ◽  
Author(s):  
Hamza Gharsellaoui ◽  
Mohamed Khalgui ◽  
Samir Ben Ahmed
Keyword(s):  
Response Time ◽  
Real Time ◽  
Dynamic Scheduling ◽  
Optimal Algorithm ◽  
Real Life ◽  
Sporadic Tasks ◽  
Periodic Tasks ◽  
Worst Case ◽  
Utilization Factor ◽  
Earliest Deadline

This paper examines the problem of scheduling the mixed workload of both sporadic (on-line) and periodic (off-line) tasks on uniprocessor in a hard real-time environment. The authors introduce an optimal earliest deadline scheduling algorithm to optimize response time while ensuring that all periodic tasks meet their deadlines and to accept as many sporadic tasks. A necessary and sufficient schedulability test is presented, and an efficient O(n+m) guarantee algorithm is proposed. This optimal algorithm results in dynamic scheduling solutions. They are presented by a proposed intelligent agent-based architecture where a software agent is used to evaluate the response time, to calculate the processor utilization factor and also to verify the satisfaction of real-time deadlines. The agent dynamically provides technical solutions for users where the system becomes unfeasible by sending sporadic tasks to idle times, by modifying the deadlines of tasks, the worst case execution times (WCETs), the activation time, by tolerating some non critical tasks according to the (m, n) firm and a reasonable cost, or in the worst case by removing some non hard (soft) tasks according to predefined heuristic. The authors implement the agent to support these services which are applied to extensive experiments with real-life design examples in order to demonstrate the effectiveness and the excellent performance of the new optimal algorithm in normal and overload conditions.

scholarly journals Phasing of Periodic Tasks Distributed over Real-time Fieldbus

2017 ◽  
Vol 12 (5) ◽  
pp. 645 ◽  
Author(s):  
Sang-Hun Lee ◽  
Hyun-Wook Jin ◽  
Kanghee Kim ◽  
Sangil Lee
Keyword(s):  
Real Time ◽  
Search Time ◽  
Periodic Tasks ◽  
Worst Case ◽  
Real Time System ◽  
Delay Bound ◽  
End To End Delay ◽  
Global Clock ◽  
End To End ◽  
Hard Real Time

In designing a distributed hard real-time system, it is important to reduce the end-to-end delay of each real-time message in order to ensure quick responses to external inputs and a high degree of synchronization among cooperating actuators. In order to provide a real-time guarantee for each message, the related literature has focused on the analysis of end-to-end delays based on worst-case task phasing. However, such analyses are too pessimistic because they do not assume a global clock. With the assumption that task phases can be managed by using a global clock provided by emerging real-time fieldbuses, such as EtherCAT, we can try to calculate the optimal task phasing that yields the minimal worst-case end-to-end delay. In this study, we propose a heuristic to manage the phase offsets in the distributed tasks to reduce the theoretical end-to-end delay bound. The proposed heuristic reduces the search time for a solution by identifying time intervals where actual communication occurs among inter-dependent tasks. Furthermore, to analyze the distribution of endto- end delays in different phases, we implemented a simulation tool. The simulation results showed that the proposed heuristic can reduce worst-case end-to-end delay as well as jitter in end-to-end delays.

scholarly journals Online Slack-Stealing Scheduling with Modified laEDF in Real-Time Systems

Electronics ◽  
2019 ◽  
Vol 8 (11) ◽  
pp. 1286 ◽  
Author(s):  
Wonbo Jeon ◽  
Wonsop Kim ◽  
Heoncheol Lee ◽  
Cheol-Hoon Lee
Keyword(s):  
Response Time ◽  
Real Time ◽  
Execution Time ◽  
Computation Method ◽  
Periodic Tasks ◽  
Worst Case ◽  
Dynamic Priority ◽  
Look Ahead ◽  
Aperiodic Tasks ◽  
Hard Real Time

In hard real-time task systems where periodic and aperiodic tasks coexist, the object of task scheduling is to reduce the response time of the aperiodic tasks while meeting the deadline of periodic tasks. Total bandwidth server (TBS) and advanced TBS (ATBS) are used in dynamic priority systems. However, these methods are not optimal solutions because they use the worst-case execution time (WCET) or the estimation value of the actual execution time of the aperiodic tasks. This paper presents an online slack-stealing algorithm called SSML that can make significant response time reducing by modification of look-ahead earliest deadline first (laEDF) algorithm as the slack computation method. While the conventional slack-stealing method has a disadvantage that the slack amount of each frame must be calculated in advance, SSML calculates the slack when aperiodic tasks arrive. Our simulation results show that SSML outperforms the existing TBS based algorithms when the periodic task utilization is higher than 60%. Compared to ATBS with virtual release advancing (VRA), the proposed algorithm can reduce the response time up to about 75%. The performance advantage becomes much larger as the utilization increases. Moreover, it shows a small performance variation of response time for various task environments.

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