• ETRI Journal
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• 제33권2호
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• pp.230-239
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• 2011

Dynamic memory allocators for real-time embedded systems need to fulfill three fundamental requirements: bounded worst-case execution time, fast average execution time, and minimal fragmentation. Since embedded systems generally run continuously during their whole lifetime, fragmentation is one of the most important factors in designing the memory allocator. This paper focuses on minimizing fragmentation while other requirements are still satisfied. To minimize fragmentation, a part of a memory region is segregated by the proposed budgeting method that exploits the memory profile of the given application. The budgeting method can be applied for any existing memory allocators. Experimental results show that the memory efficiency of allocators can be improved by up to 18.85% by using the budgeting method. Its worst-case execution time is analyzed to be bounded.

• Journal of Computing Science and Engineering
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• 제3권1호
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• pp.59-71
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• 2009

While the average-case performance is important for general-purpose applications, worst-case performance is crucial for real-time systems to ensure schedulability and reliability. Recent work has shown that simple prefetching techniques such as the Next-N-Line prefetching can benefit both average-case and worst-case performance; however, the improvement on the worstcase execution time (WCET) is rather limited and inefficient. This paper presents two instruction prefetching approaches that are specially designed to enhance the worst-case performance, including the loop-based prefetching and WCET-oriented prefetching. Our experiments indicate that both instruction prefetching techniques can achieve better worst-case execution cycles than the Next-N-Line prefetching while having various impacts on the average-case performance.

• 정보처리학회논문지A
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• 제11A권4호
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• pp.243-250
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• 2004

실시간 시스템은 시스템이 적시성을 보장하는지 파악하기 위해 실시간 감시기법을 이용한다. 일반적으로 실시간 감시는 실시간 시스템의 현재 동작상태를 파악하는데 중점을 두는 기법이다. 그러나 실시간 시스템의 안정적인 수행을 지원하기 위해서는, 현재 상태를 파악하는 것뿐 아니라, 실시간 시스템 및 시스템상에서 동작하는 실시간 프로세스들의 수행도 예측할 수 있어야 한다. 그러나 기존 예측모델을 실시간 감시기법에 적용하기에는 몇 가지 한계가 있다. 첫째, 예측기능은 실시간 프로세스가 종료한 시점에서 정적인 분석을 통해 수행된다. 둘째, 예측을 위해 사전 기초 통계분석이 필요하다. 셋째, 예측을 위한 이전확률 및 클러스터 정보가 현재 시점을 정확하게 반영하지 못한다. 본 논문에서는 이러한 문제점들을 해결하고 실시간 감시기법에 적용할 수 있는 학습 기반의 수행 예측모델을 제안한다. 이 모델은 학습기법을 통해 불필요한 전처리과정을 없애고, 현시점의 데이터를 이용해, 보다 정확한 실시간 프로세스의 수행 예측이 가능하도록 한다. 또한 이 모델은 실시간 프로세스 수행 시간의 증가율 분석을 통해 다단계 예측을 지원하며, 무엇보다 실시간 프로세스가 실행되는 동안 예측이 가능한 동적 예측을 지원하도록 설계하였다. 실험 결과를 통해 훈련집합의 크기가 10 이상이면 80% 이상의 판단 정확도를 보이며, 다단계 예측의 경우, 훈련집합의 크기 이상의 수행 횟수를 넘으면 다단계 예측의 예측 차는 최소화되는 것으로 나타났다. 본 논문에서 제안한 예측모델은 가장 단순한 학습 알고리즘을 적용했다는 점과, CPU, 메모리, 입출력 데이터를 다루는 다차원 자원공간 모델을 고려하지 못한 한계가 있어 향후에 관련 연구가 요구된다. 본 논문에서 제안하는 학습기반 수행 예측모델은 실시간 감시 및 제어를 필요로 하는 분야 및 응용 분야에 적용할 수 있다.

• International Journal of Internet, Broadcasting and Communication
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• 제16권3호
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• pp.363-369
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• 2024

In this paper, we develope a LOB(Limit Order Book) analyzing tool for an automated trading system, which features real-time and offline analysis of LOB data in conjunction with execution data. The 10-tier LOB data analyzer developed in this paper, which contains ask/bid prices and the execution data, receivs transaction requests in real-time from the Kiwoom Open API+ server. In the OnReceiveTrData event, the transaction data from the server is received and processed. The real-time data, triggered by the transaction, is received and processed in the OnReceiveRealData event. These two types of data are stored in a database and replayed in the same way as if it were a real-time situation in simulation mode. The LOB data are selectively read and analyzed in a necessary time points. The tool provides various features such as bar chart analysis and pattern analysis of the total shares on the bid side and ask side, which are used to develop a tool to accurately determine the timing of stock trading.

• Management Science and Financial Engineering
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• 제8권1호
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• pp.53-75
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• 2002

In this Paper, an attempt is made to establish a learning framework for robust planning and real-time execution control. Necessary definitions and concepts are clearly presented to describe real-time operational control in response to Plan disruptions. A general mathematical framework for disruption recovery is also laid out. Global disruption model is decomposed into suitable number of local disruption models. Execution Pattern is designed to capture local disruptions using decomposed-reverse neural mappings, and to further demonstrate how the decomposed-reverse mappings could be applied for solving disrubtion recovery problems. Two decomposed-reverse neural mappings, N-K-M and M-K-N are employed to produce transportation solutions in react-time. A potential extension is also discussed using the proposed mapping principle and other hybrid heuristics. Experimental results are provided to verify the proposed approach.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.670-686
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• 2017

MapReduce (MRV1), a popular programming model, proposed by Google, has been well used to process large datasets in Hadoop, an open source cloud platform. Its new version MapReduce 2.0 (MRV2) developed along with the emerging of Yarn has achieved obvious improvement over MRV1. However, MRV2 suffers from long finishing time on certain types of jobs. Speculative Execution (SE) has been presented as an approach to the problem above by backing up those delayed jobs from low-performance machines to higher ones. In this paper, an adaptive SE strategy (ASE) is presented in Hadoop-2.6.0. Experiment results have depicted that the ASE duplicates tasks according to real-time resources usage among work nodes in a cloud. In addition, the performance of MRV2 is largely improved using the ASE strategy on job execution time and resource consumption, whether in a multi-job environment.

• 정보과학회 컴퓨팅의 실제 논문지
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• 제23권4호
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• pp.199-209
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• 2017

최근 실시간 임베디드 시스템 분야에서 가상화를 이용한 시스템 통합에 대한 관심이 꾸준히 증가하고 있다. 가상화 기술은 하이퍼바이저의 개입으로 인한 오버헤드를 수반하며 이는 가상 머신 상에서 구동되는 프로그램의 수행시간을 증가시킨다. 수행시간이 증가함에 따라 가상 머신 상에 있는 소프트웨어의 성능이 하락하며, 실시간성을 유지하기 어려워진다. 본 논문에서는 이러한 문제를 해결하기 위해 가상머신 상의 프로그램이 하이퍼바이저의 개입 없이 직접 물리적인 자원에 접근할 수 있도록 하이퍼바이저를 설계하고 구현하였으며 이를 K-Hypervisor라 부른다. 실험 결과에 따르면 K-Hypervisor 상에서 구동되는 프로그램들의 수행시간은 네이티브 환경에서 측정된 결과와 비교하여 평균적으로 약 3% 정도 증가한다. 또한 성능 저하가 태스크가 접근하는 자원의 종류나 빈도와 관계없이 항상 일정하여 소프트웨어의 실시간성을 유지하기에 적합하다.

• 대한임베디드공학회논문지
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• 제12권4호
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• pp.205-212
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• 2017

Linux Foundation has announced a real-time kernel, called Zephyr, for IoT applications recently. Zephyr kernel provides synchronous and asynchronous IPC for data communication between threads. Synchronous IPC is useful for programming multi-threads that need to be executed synchronously, since the sender thread is blocked until the data is delivered to the receiver thread and the completion of data transfer can be known to two threads. In general, 'IPC execution time' is defined as the time duration between the sender thread sends data and the receiver thread receives the data sent. Especially, it is important that 'IPC execution time' in the synchronous IPC should be fixed in real-time kernel like Zephyr. However, we have found that the execution time of the synchronous IPC in Zephyr kernel increases in proportion to the number of threads executing in the kernel. In this paper, we propose a method to implement a fixed time synchronous IPC in Zephyr kernel using Direct Thread Switching(DTS) technique. Using the technique, the receiver thread executes directly after the sender thread sends a data during the remaining time slice of the sender thread and we can archive a fixed IPC execution time even when the number of threads executing in the kernel increases. In this paper, we implemented synchronous IPC using DTS in the Zephyr kernel and found the IPC execution time of the IPC is always 389 cycle that is relatively small and fixed.

• 로봇학회논문지
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• 제7권4호
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• pp.292-298
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• 2012

It is a real-time system that the system correctness depends not only on the correctness of the logical result of the computation but also on the result delivery time. Real-time Operating System (RTOS) is a software that manages the time of a microprocessor to ensure that the most important code runs first so that it is a good building block to design the real-time system. The real-time performance is achieved by using real-time mechanisms through data communication and synchronization of inter-task communication (ITC) between tasks. Therefore, test on the response time of real-time mechanisms is a good measure to predict the performance of real-time systems. This paper aims to analysis the response characteristics of real-time mechanisms in kernel space for real-time embedded Linux: RTAI and Xenomai. The performance evaluations of real-time mechanism depending on the changes of task periods are conducted. Test metrics are jitter of periodic tasks and response time of real-time mechanisms including semaphore, real-time FIFO, Mailbox and Message queue. The periodicity of tasks is relatively consistent for Xenomai but RTAI reveals smaller jitter as an average result. As for real-time mechanisms, semaphore and message transfer mechanism of Xenomai has a superior response to estimate deterministic real-time task execution. But real-time FIFO in RTAI shows faster response. The results are promising to estimate deterministic real-time task execution in implementing real-time systems using real-time embedded Linux.

• Journal of Electrical Engineering and information Science
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• 제1권1호
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• pp.118-128
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• 1996

In safety critical hard real-time systems, a timing fault may yield catastrophic results. In order to eliminate the timing faults from the fast responsive real-time control systems, it is necessary to schedule a code based on high precision timing analysis. Further, the schedulability enhancement by having multiple processors is of wide spread interest. However, although an instruction level parallel processing is quite effective to improve the schedulability of such a system, none of the real-time applications employ instruction level parallel scheduling techniques because most of the real-time scheduling models have not been designed for fine-grain execution. In this paper, we present a timing constraint model specifying high precision timing constraints, and a practical approach for constructing static schedules for a VLIW execution model. The new model and analysis can guarantee timing accuracy to within a single machine clock cycle.