• Proceedings of the Korean Information Science Society Conference
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• 2010.06b
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• pp.389-392
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• 2010

실시간 임베디드 시스템에서 멀티미디어 시스템 같은 빠른 응답성을 요구하는 시스템이 존재 할 수 있다. 현재 EDF, RM 알고리즘의 경우 각각 마감시간, 수행 주기 시간에 의해서 우선순위가 선정되고 수행된다. 그러나 시스템 상에 실시간 프로세스 외에 다양한 프로세스가 존재할 수 있다. 본 논문에서는 마감 시간과 프로세스의 기본 우선순위를 고려하여 새로운 우선순위를 이용하며, 전체 프로세스들이 마감 시간내에 스케줄링 가능하고 문맥교환에 의한 오버헤드에 의해 마감시간을 넘어가지 않을 경우 각 프로세스들에게 타임 슬라이스를 할당하여 수행할 수 있도록 하여 기존 알고리즘들 보다 응답성을 향상시키는 기법을 제시한다.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.373-375
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• 2002

본 논문은 실시간 운영체제에서 프로세스의 효율적인 관리를 위한 스케줄링 알고리즘을 제안한다. 따라서 CPU의 활용도를 높이고 스케줄링 시간과 인터럽트 시간을 줄임으로서 자원을 효율적으로 관리할 수 있다. 본 논문에서 제안하는 방법으로는 다중 큐에 PIT(Process Information Table)를 두어 각각의 큐에 프로세스가 들어오면 우선순위에 따라 CPU를 할당하는 방법이다. 기존의 다중 큐와는 달리 우선순위 프로세스를 보다 정확하고 빨리 찾아내어 외부 또는 내부의 인터럽트에 응답 할 수 있게 하였다. 또한 우선순위에 밀려 실행하지 못하는 프로세스는 일정 시간이 경과하면 CPU를 선점할 수 있다. 그러므로 CPU는 활용도가 높아지고 유휴 시간은 짧아지게 된다. 본 논문은 일반 펜티엄 PC에서 실험하였으며 현재 사용되는 RTOS(VxWorks, QNX)와 비교하여 다소 우수함을 보였다.

• The Journal of the Korea Contents Association
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• v.10 no.1
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• pp.94-102
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• 2010

In recent years, embedded systems such as cellular phones, Portable Multimedia Player, intelligent appliance, automobile engine control are reshaping the way people live, work, and play. Thereby, services application to guarantee various requirements of users become increasingly sophisticated and complicated, such embedded computing platforms use real-time operating systems (RTOSs) with time determinism. These RTOSs must not only provide predictable services but must also be efficient and small in size. Kernel services should also be deterministic by specifying how long each service call will take to execute. Having this information allows the application designers to better plan their real-time application software so as not to miss the deadline of each task. In this paper, we present the complete generalized real-time scheduling algorithm using multi-dimensional methodology to determine the highest priority in the ready list with 2r levels of priorities in a constant time without additional memory overhead.

• The Journal of the Korea Contents Association
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• v.9 no.12
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• pp.52-63
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• 2009

The problem of scheduling simply periodic task systems upon a uniform multiprocessor is considered. Partitioning of periodic task systems requires solving the bin-packing problem, which is known to be intractable (NP-hard in the strong sense). This paper presents a global scheduling algorithm which transforms a given simply periodic task system into another using a "task-splitting" technique. Each transformed simply periodic task system is guaranteed to be successfully scheduled upon any uniform multiprocessor using a partitioned scheduling algorithm. It is proven that the proposed algorithm achieves the theoretical maximum utilization bound upon any uniform multiprocessor platform.

• 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.

• Journal of Internet Computing and Services
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• v.12 no.5
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• pp.1-9
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• 2011

Wireless mobile networks that exploit generalized PF scheduling can dynamically allocate network resources by using scheduling parameters. There are limitations to predict throughputs by the conventional stochastic approach in general. Moreover the limitations make it difficult to find appropriate scheduling parameters for achieving the demanded throughputs. This paper derives a prediction algorithm that predicts throughputs of the networks by using deterministic approach. A throughput adjust algorithm and a throughput switching algorithm are derived from the prediction algorithm. The performance of the throughput prediction/switching algorithms is evaluated by a simulator based on IEEE 802.16m system.

• Journal of KIISE:Software and Applications
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• v.31 no.3
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• pp.293-307
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• 2004

We consider the problem of scheduling tasks of a precedence constrained task graph, where each task has its execution time and deadline, onto a set of identical processors in a way that simultaneously minimizes the number of processors required and the total tardiness of tasks. Most existing approaches tend to focus on the minimization of the total tardiness of tasks. In another methods, solutions to this problem are usually computed by combining the two objectives into a simple criterion to be optimized. In this paper, the minimization is carried out using a multiobjective genetic algorithm (GA) that independently considers both criteria by using a vector-valued cost function. We present various GA components that are well suited to the problem of task scheduling, such as a non-trivial encoding strategy. a domination-based selection operator, and a heuristic crossover operator We also provide three local improvement heuristics that facilitate the fast convergence of GA's. The experimental results showed that when compared to five methods used previously, such as list-scheduling algorithms and a specific genetic algorithm, the Performance of our algorithm was comparable or better for 178 out of 180 randomly generated task graphs.

• The KIPS Transactions:PartA
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• v.10A no.3
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• pp.181-188
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• 2003

We propose a heuristic on-line scheduling algorithm for the IRIS (Increasing Reward with Increasing Service) tasks, which has low computation complexity and produces total reward approximated to that of previous on-line optimal algorithms. The previous on-line optimal algorithms for IRIS tasks perform scheduling on all tasks in a system to maximize total reward. Therefore, the complexities of these algorithms are too high to apply them to practical systems handling many tasks. The proposed algorithm doesn´t perform scheduling on all tasks in a system, but on (constant) W´s tasks selected by a predefined task selection policy. The proposed algorithm is based on task selection policies that define how to select tasks to be scheduled. We suggest two simple and intuitive selection policies and a generalized selection policy that integrates previous two selection policies. By narrowing down scheduling scope to only W´s selected tasks, the computation complexity of proposed algorithm can be reduced to O(Wn). However, simulation results for various cases show that it is closed to O(W) on the average.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.05a
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• pp.487-490
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• 2003

본 논문은 동적 우선순위 실시간 시스템에서 경성 종료시한을 갖는 비주기 태스크를 스케줄링하는 EDL 알고리즘을 확장하여 구현하였다. 동적 우선순위 방식의 비주기 태스크를 스케줄링 하는데 있어서 최적이라고 증명된 EDL 알고리즘이 갖고 있는 문제점인 실행되고 있는 비주기 태스크가 있으며 다음 비주기 태스크의 요청이 들어왔을 때 선행된 비주기 태스크의 종료시점에서 받아들이는 제약을 개선하고 경성 비주기 태스크들이 동시에 들어왔을 때의 응답시간을 시분할 방식을 이용하여 최소화하였다.

• The KIPS Transactions:PartA
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• v.11A no.7 s.91
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• pp.547-554
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• 2004

To play back CM (Continuous Media) in online mode, the multimedia system Is required to have a real-time disk scheduling scheme that can efficiently fulfill the strict temporal constraints of serviced CM streams to prevent hiccups. In general, such disk scheduling is performed based on the concept of periodic prefetching since a CM stream has a rather long Playback time. In this paper, we also propose a periodic prefetching scheme that runs by using real-time disk channels, called on-time delivery channels. Since the channels are generated from the bulk-SCAN algorithm and they can be allocated in a very flexible manner based on the EDF (earliest-deadline-first) algorithm, the proposed scheme provides a better Performance in terms of I/O throughput and the average response time, as well as hiccup-free playback of concurrent CM streams. To show that the proposed scheme outperforms other methods, we give some simulation results.