• Journal of KIISE:Computer Systems and Theory
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• v.29 no.9
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• pp.520-529
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• 2002

This paper presents an approach for scheduling network messages with real-time dynamic algorithms. We present the method that calculates an intermediate relative deadline of the message based on the EDF(Earliest Deadline First) scheduling policy. We adjust the slack of message by using this intermediate relative deadline to allocate a priority of message. The priority of the message can be determined accurately by using the slack that calculates in our approach, which increases the schedulability efficiency of the message. As a result, we reduce the worst-case response time and improve the guarantee ratio of real-time messages. Also, we describe the analysis method to check the schedulability on message sets, and show the efficiency of our approach by comparing the results of the DM(Deadline Monotonic) approach and the existing EDF approach with that of the improved EDF in our approach through the simulation.

• The KIPS Transactions:PartA
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• v.16A no.6
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• pp.437-442
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• 2009

For multiprocessor systems, Earliest Deadline First (EDF) based on deadline and Least Laxity First (LLF) based on laxity are not suitable for practical environment since EDF has low schedulability and LLF has high context switching overhead. As a combining of EDF and LLF to improve the performance, Earliest Deadline Zero Laxity (EDZL) was proposed. EDZL is basically the same as EDF. But if the laxity of a task becomes zero, its priority is promoted to the highest level. In this paper, we propose Least Laxity Zero Laxity (LLZL) which is based on LLF. But context switching is allowed only if the laxity of a task on rady queue becomes zero. Simulation results show that LLZL has high schedulability approaching to LLF and low context switching overhead similar to EDF. In comparison with EDZL, LLZL has better performance in both of schedulability and context switching overhead.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.7
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• pp.368-376
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• 2005

Multiprocessor architecture becomes increasingly common on real-time systems as computer hardware technology rapidly progresses and the workload of real-time systems increases. However, efficient solutions for many real-time multiprocessor scheduling problems are not known. Hence many researchers apply uniprocessor scheduling algorithms to multiprocessor scheduling or devise new algorithms based on these algorithms. Such algorithms are EDF (Earliest Deadline First), LLF (Least Laxity First), EDF-US[m/(2m-1)], and EDZL (Earliest Deadline Zero Laxity), and comparative studies on them are necessary. In this paper, we show the dominance relation of these algorithms with respect to schedulability, and we prove EDZL strictly dominates EDF. The simulation results show that EDZL has high processor utilization and it causes a small number of preemptions.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.370-372
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• 2002

다중처리기 상에서 실시간 태스크 스케줄링에 대한 연구가 현재 많이 수행되고 있지만, 주로 Pfair(P-fairness)와 EDF(Earliest Deadline First) 알고리즘에 대한 연구이다. Pfair는 이론적인 연구에 초점을 두고 있으며, EDF는 처리기들을 효율적으로 이용하지 못하는 문제점을 가지고 있다. 본 논문에서는 다중처리기 상의 주기적인 실시간 태스크 집합을 대상으로, LLA(Least Laxity Algorithm) 알고리즘이 높은 스케줄링 가능성(schedulability)을 가짐을 먼저 보인다. 다음으로 기존 알고리즘들의 문제점을 보완하기 위해 EDF와 LLA를 결합한 ED/LL(Earliest Deadline/Least Laxity)이라는 알고리즘을 제시한다. ED/LL은 LLA보다 문맥교환 횟수는 적고 EDF보다 스케줄링 가능성이 높으며, 구현 오버헤드도 크지 않다.

• Journal of Internet Computing and Services
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• v.8 no.1
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• pp.71-78
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• 2007

In this paper, an effective task scheduling scheme was proposed for the flexible real time LINUX systems with the selection between EDF(earliest deadline first) and RMS(rate monotonic scheduling). It was known that many task scheduling schemes were analyzed according to the characteristics of scheduling schemes and the guarantee of an earliest deadline scheduler for process utilities.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.7
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• pp.1363-1370
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• 2009

Recently, the automobile industry is going through drastic environmental changes. The relative importance of information technology rapidly developed so far is getting heavier as it is grafted to electrical and electronic areas among all other automobile-related technologies. In this paper, an improved algorithm from the real-time scheduling algorithm of operation system which is loaded in embedded system will be presented. The number of wait-queue of priority was reduced from 16 to 4 in the parts where wide differences were shown in scheduling algorithm of the existing OSEK OS. While the FIFO algorithm was used in wait-queue, the EDF algorithm was applied to the proposed scheduling algorithm, which more improved the real-timeness. Also a simple experiment on the proposed scheduling algorithm was conducted.

• Journal of Korea Multimedia Society
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• v.7 no.9
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• pp.1273-1281
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• 2004

There have been a number of researches on real-time packet scheduling based on EDF algorithm to support end-to-end delay bound guarantees for real-time traffic transmission. However, EDF-based packet scheduler could not guarantee the real-time requirements of real-time traffic if there exist non-real-time traffic. In this paper, we propose a new admission control algorithm and packet scheduling scheme considering non-real-time traffic in the real -time packet scheduler based on EDF policy. Proposed admission control algorithm has pseudo-polynomial time complexity, but we show through simulation that it can be used with little run-time overhead.

• Journal of Internet Computing and Services
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• v.6 no.2
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• pp.25-35
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• 2005

The Rate Monotonic(RM) scheduling algorithm and Earliest Deadline First(EDF) scheduling algorithm are normally used in Real-Time scheduling algorithm. In those scheduling algorithm, we could predict the performance possibility with total utilization value of task group. But. it had problems with prediction of the boundedness in individual task when the utilization value was over in temporary task. In this paper, the suggested scheduling algorithm can predict task when the utilization value was over and it suggested the method of predicting scheduling possibility based on the utilization value of individual task as well. it predicted the boundedness of scheduling possibility test through simulation In Real-Time scheduling algorithm and analyzed the result.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06b
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• pp.388-393
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• 2008

유비쿼터스 지능 공간 환경에서 중요한 이슈는 사용자에게 현재 상황에 최적의 서비스를 제공하는 것이며, 이를 위해서 상황 인식(Context Aware) 기법에 대한 연구가 널리 진행되고 있다. 유비쿼터스 지능 공간은 분산 배치된 수많은 애플리케이션 및 장치와 같은 스마트 객체들이 존재하여 사용자에게 최적의 서비스를 제공하는 환경이다. 유비쿼터스 지능 공간에서는 각 스마트 객체가 수집하는 데이터는 무수히 많다. 사용자에게 최적의 서비스를 제공하기 위해선 데이터들을 빠르게 처리하여 서비스를 제공하여야 한다. 현재 연구된 스케줄링 방법은 데이터 처리에만 중점을 두었기 때문에 스스로 상황을 인지하여 예측하여야 하는 유비쿼터스 지능 공간을 위한 미들웨어에는 적합하지 않다. 본 논문은 수집한 데이터를 바탕으로 상황을 인식하고 태스크의 우선순위를 재조정하는 상황 인지형 실시간 스케줄링 기법을 제안한다. 제안하는 상황 인지형 실시간 스케줄링 기법인 U-RM, U-EDF와 기존의 RM, EDF 알고리즘을 비교하여 성능평가를 한 결과 U-RM은 기존의 RM보다 최대 20.7%의 성능 향상을 보였으며, U-EDF의 경우 기존의 EDF 보다 최대 26.8%의 성능 향상을 보였다.

• The KIPS Transactions:PartA
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• v.18A no.4
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• pp.143-150
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• 2011

This paper presents an EDF based scheduling algorithm for scheduling imprecise computation model where each task consists of mandatory part and optional part. Imprecise computation is useful to manage overload condition. In overload situation, some optional parts should be removed. The proposed DOP algorithm removes optional parts of earlier deadline tasks to enhance flexibly for newly arriving tasks. A simulation result shows that DOP has better performance than other algorithms.