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Integration of Task Offloading, CPU Voltage Scaling, and Memory Placement for Power-Saving in Mobile Real-Time Systems
Soomin Ki, Gyuri Byun, Kyungwoon Cho, Hyokyung Bahn
http://doi.org/10.5626/JOK.2022.49.11.919
In this paper, we study real-time task scheduling that aims to minimize power consumption of CPU, memory, and network devices in mobile systems. By defining extended task model and adopting three low-power techniques (i.e., task offloading, CPU voltage scaling, and low-power memory placement), we co-optimize these three techniques, thereby saving power consumption of real-time systems by 76.8% on average. Our scheduling has the ability of rescheduling real-time task set by reconfiguring offloading, DVFS, and memory placement considering variations of network conditions, thereby minimizing power consumption without missing deadlines of given real-time tasks.
Analysis of Limits in Applying AP-QoS-based Wi-Fi Slicing for Real-Time Systems
Jin Hyun Kim, Hyonyoung Choi, Gangjin Kim, Yundo Choi, Tae-Won Ban, Se-Hoon Kim
http://doi.org/10.5626/JOK.2021.48.6.723
Network slicing is a new network technology that guarantees the quality of network services according to application services or user’s types. Wi-Fi, IEEE 802.11-based LAN, is the mostly popularly used short-range wireless network and has been continually attracting more and more from users. Recently, the use of Wi-Fi by safety critical IoT devices, such as medical devices, has been drastically increasing. Moreover, enterprises require network slicing of Wi-Fi to introduce the provision of prioritized QoS of Wi-Fi depending on the service type of customer. This paper presents the analysis of the limits and difficulties in applying AP-QoS-based network slicing for hard real-time systems that demand temporal deterministic streaming services. In this paper, we have defined a formal framework to analyze QoS-providing IEEE 802.11e Enhanced Distributed Coordination Access and provide the worst-case streaming scenarios and thereby demonstrated why the temporal determinism of network streaming is broken. In addition, simulation results of AP-QoS-based network slicing using NS-3 are presented to show the limits and difficulties of the network slicing. Moreover, we present Wi-Fi network slicing techniques based on EDCA of AP-QoS for real-time systems through our technical report referenced in this paper.
ILP-based Schedule Synthesis of Time-Sensitive Networking
Jin Hyun Kim, Hyonyoung Choi, Kyong Hoon Kim, Insup Lee, Se-Hoon Kim
http://doi.org/10.5626/JOK.2021.48.6.595
IEEE 802.1Qbv Time Sensitive Network (TSN), the latest real-time Ethernet standard, is a network designed to guarantee the temporal accuracy of streams. TSN is an Ethernet-based network system that is actively being developed for the factory automation and automobile network systems. TSN controls the flow of data streams based on schedules generated statically off-line to satisfy end-to-end delay or jitter requirements. However, the generation of TSN schedules is an NP-hard problem; because of this, constraint solving techniques, such as SMT (Satisfiability Modulo Theory) and ILP (Integer Linear Programming), have mainly been proposed as solutions to this problem. This paper presents a new approach using a heuristic greedy and incremental algorithm working with ILP to decrease the complexity of computing schedules and improve the schedule generation performance in computing TSN schedules. Finally, we compare our proposed method with the existing SMT solver approach to show the performance of our approach.
Formal Model Design for Network and Operating System Behaviors in Real-time Distributed System Verification with Coq
http://doi.org/10.5626/JOK.2020.47.11.1071
Improving the safety and reliability of distributed systems using formal verification methods is an urgent problem. As many of these distributed systems are safety-critical, such as medical or avionics systems, failures of these systems may cause catastrophic results. However, applying formal verification to distributed systems requires not only execution semantics in software, but also behavioral models of the environments, including the operating systems and network involved. We designed a formal abstract model of network and operating system behaviors with the Coq proof assistant. This model consists of local-site execution semantics that model a single computer, the composition of these local-site semantics along with a message exchange model constitutes the global system semantics. We applied and tested this model to verify its applicability when used in a simple server-client system. We expect this model to be used in the verification of practical systems.
Scenario-Based Multi-core Multi-tasking of Engine Control Unit Real-Time Object-Oriented Model
http://doi.org/10.5626/JOK.2020.47.4.352
This paper proposes a method for the efficient execution of real-time object-oriented models in multi-core systems using a vehicle Engine Control Unit (ECU) system as a case study. All current commercial and open source real-time object-oriented modeling tools use objects as basic units of mapping to tasks and cores. In contrast, we propose a method of using scenarios instead of objects as the basic units of mapping. To demonstrate the efficiency of the proposed method, we used an ECU system model and eTrice, which is the only free open source among real-time object-oriented modeling tools. Specifically, we implemented an ECU real-time object-oriented model in eTrice, and extended the implementation of eTrice Linux run-time systems and code generators to support scenario-based architecture and multi-core synchronization mechanisms. Our results demonstrate that the proposed scenario-based multi-core multi-tasking improves both theoretical and experimental response spare times (slacks) compared with current and previous work.
Deadline Task Scheduling for Mitigating the CPU Performance Interference in Android Systems
Jeongwoong Lee, Taehyung Lee, Young Ik Eom
http://doi.org/10.5626/JOK.2020.47.1.11
In the Android Linux kernel, most of the tasks are expected to run fairly, and so, there can be delays in processing time-sensitive applications. In particular, since the user may feel inconveniences when the delay occurs in media data processing or biometrics processing such as fingerprint recognition, the tasks requiring completion within a given time should be considered as deadline tasks. However, using the deadline scheduler in current Android systems can cause two problems. First, as deadline tasks come to the system and are executed, the CPU energy consumption can be increased. Second, the high priority of the deadline tasks can cause performance degradation of the normal tasks. To mitigate these problems, this paper proposes a method of scheduling deadline tasks on Android systems, which reduces the performance impact on normal tasks, while trying to minimize energy consumption. Our evaluation on the CPU benchmark shows that the proposed method improves the CPU performance by about 10% compared with the conventional deadline scheduler, but does not increase power consumption by effectively utilizing CPU frequency.
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