• IEMEK Journal of Embedded Systems and Applications
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• v.1 no.2
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• pp.90-103
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• 2006

There are many file systems in various operating systems. Those are usually designed for server environments, where the common cases are usually 'multiple active users', 'great many small files' And they assume a big main memory to be used as buffer cache. So the existing file systems are not suitable for resource hungry embedded systems that process multimedia data streams. In this study, we designed and implemented a new file system which efficiently stores and retrieves multimedia data steams. The proposed file system has a very simple disk layout, which guarantees a quick disk initialization and file system recovery. And we introduced a new indexing-scheme, called the time-based indexing scheme, with the file system. With the indexing scheme, the file system maintains the relation between time and the location for all the multimedia streams. The scheme is useful in searching and playing the compressed multimedia streams by locating exact frame position with given time, resulting in reduction of CPU processing and power consumption. The proposed file system and its APIs utilizing the time-based indexing schemes were implemented firstly on a Linux environment, though it is operating system independent. In the performance evaluation on a real DVR system, which measured the execution time of multi-threaded reading and writing, we found the proposed file system is maximum 38.7% faster than EXT2 file system.

• International journal of advanced smart convergence
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• v.6 no.1
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• pp.26-31
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• 2017

When mobile navigator device accesses data randomly, the cache memory performance is rapidly deteriorated due to low memory access locality. For instance, GPS (General Positioning System) of navigator program for automobiles or drones, that are currently in common use, uses data from 32 satellites and computes current position of a receiver. This computation of positioning is the major part of GPS which accounts more than 50% computation in the program. In this computation task, the satellite signals are received in real time and stored in buffer memories. At this task, since necessary data cannot be sequentially stored, the data is read and used at random. This data accessing patterns are generated randomly, thus, memory system performance is worse by low data locality. As a result, it is difficult to process data in real time due to low data localization. Improving the low memory access locality inherited on the algorithms of conventional communication applications requires a certain optimization technique to solve this problem. In this study, we try to do optimizations with data and memory to improve the locality problem. In experiment, we show that our case study can improve processing speed of core computation and improve our overall system performance by 14%.

• The Transactions of the Korea Information Processing Society
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• v.5 no.1
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• pp.24-32
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• 1998

The bus contention among bus-based shared-memory multiprocessors limits their performance. In addition, under split bus transaction environment, multiprocessors may make some memory requests unnecessary stand by in the memory access buffer, which makes system performance worse. This unnecessary stand-by can be eliminated by maintaining the bitmap table which contains the status bit for each memory block. However, this mechanism requires a great size of SRAM for the status information, which is fully mapped from the whole memory blocks. To solve this problem, we propose a bitmap cache which exploits partial mapping and locality of references. The simulation results show that the proposed system can greatly reduce the capacity of SRAM for the status information with little deteriorating its performance.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.11a
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• pp.702-705
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• 2017

최근 들어 개인정보 보호의 중요성에 대한 인식이 높아지고 있다. 개인정보 위협 요소 증가 및 유출 사고 증가 등으로 개인정보 보호 필요성이 높아지고 있으며, 개인정보보호법 발효 및 시행에 따른 기술적 보호 마련을 위하여 외국계 카드 발행사에서 지속적으로 PCI DSS(Payment Card Industry Data Security Standard)의 준수를 요청하고 있다. 카드 소유자의 데이터를 전송, 처리, 저장하는 환경에 대한 인증으로 적격업체 선정의 자격을 주기도 한다. 이러한 보안성 심의 기준이 강화되고 있으나 DB 암호화 제품인 TDE(Transparent Data Encryption) 방식의 암호화 방법은 암호화 기능 이외에 접근제어, 키 기밀성 보장을 위한 옵션의 추가 도입 검토가 필요하며, 서비스를 위해서 DB 전용 메모리 영역(SGA)의 Buffer Cache에 평문(Plain Text)으로 복호화한 후 로드하여 사용하므로 예상치 못한 또 다른 심각한 데이터 유출의 위험이 있다. 본 논문에서는 개인정보 암호화 방법을 연구하고 구현과정에서 발생한 문제에 대한 해결 과정을 설명하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.10
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• pp.2430-2447
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• 2013

In recent years, HTTP adaptive streaming (HAS) has attracted considerable attention as the state-of-the-art technology for video transport. HAS dynamically adjusts the quality of video streaming according to the network bandwidth and device capability of users. Content-Centric Networking (CCN) has also emerged as a future Internet architecture, which is a novel communication paradigm that integrates content delivery as a native network primitive. These trends have led to the new research issue of harmonizing HAS with the in-network caching provided by CCN routers. Previous research has shown that the performance of HAS can be improved by using the H.264/SVC(scalable video codec) in the in-network caching environments. However, the previous study did not address the misbehavior that causes video freeze when overestimating the available network bandwidth, which is attributable to the high cache hit rate. Thus, we propose a new SVC-based adaptation algorithm that utilizes a drop timer. Our approach aims to stop the downloading of additional enhancement layers that are not cached in the local CCN routers in a timely manner, thereby preventing excessive consumption of the video buffer. We implemented our algorithm in the SVC-HAS client and deployed a testbed that could run Smooth-Streaming, which is one of the most popular HAS solutions, over CCNx, which is the reference implementation of CCN. Our experimental results showed that the proposed scheme (SLA) could avoid video freeze in an effective manner, but without reducing the high hit rate on the CCN routers or affecting the high video quality on the SVC-HAS client.

• Journal of KIISE
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• v.41 no.10
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• pp.832-837
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• 2014

Application loading speed can be improved by timely prefetching disk blocks likely to be needed by an application. However, existing prefetchers -- if they are not specialized to a particular application -- incur high overheads and are poor at identifying the blocks that will actually be required. There are many sequences in which blocks may be needed and, even if two access sequences are identical, block tracing and access timings can be affected significantly by the state of the buffer cache. We propose a new application-independent software-based prefetching technique, in which breakpoints are inserted at appropriate places in an application to collect the information on correlations between the blocks and to prefetch the potential blocks ahead of their schedule based on it. Experiments on an HDD-based desktop PC demonstrated an average 30% reduction in application launch time and 15% in general I/O, while reducing the wasted overhead.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.149-155
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• 2012

SSD is a storage device of having high-performance controller and cache buffer and consists of many NAND flash memories. Because NAND flash memory does not support in-place update, valid pages are invalidated when update and erase operations are issued in file system and then invalid pages are completely deleted via garbage collection. However, garbage collection performs many erase operations of long latency and then it reduces I/O performance and increases wear leveling in SSD. In this paper, we propose a new method of de-duplicating valid data and recycling invalid data. The method de-duplicates valid data and then recycles invalid data so that it improves de-duplication ratio. Due to reducing number of writes and garbage collection, the method could increase I/O performance and decrease wear leveling in SSD. Experimental result shows that it can reduce maximum 20% number of garbage collections and 9% I/O latency than those of general case.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.12
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• pp.57-64
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• 2008

In this paper, we propose a system-level simulator for the performance analysis of a Solid-State Disk (SSD) in PC environment by using TLM (Transaction Level Modeling) method. Our method provides quantitative analysis for a variety of architectural choices of PC system as well as SSD. Also, it drastically reduces the analysis time compared to the conventional RTL (Register Transfer Level) modeling method. To show the effectiveness of the proposed simulator, we performed several explorations of PC architecture as well as SSD. More specifically, we measured the performance impact of the hit rate of a cache buffer which temporarily stores the data from PC. Also, we analyzed the performance variation of SSD for various NAND Flash memories which show different response time with our simulator. These experimental results show that our simulator can be effectively utilized for the architecture exploration of SSD as well as PC.

• Journal of Internet Computing and Services
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• v.8 no.2
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• pp.77-87
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• 2007

A typical VOD service allows that a number of remote clients playback a desired video from a large collection of videos stored in one or more video servers. The main bottleneck for a VOD service is the network bandwidth connecting to the VOD server to the client due to the high bandwidth requirements. Many previous researches have shown that VOD server can be greatly improved through the use of multicast, broadcast, or P2P scheme. Broadcast is one of the most efficient techniques because it can transmit a stream to many users without additional network bandwidth. But the broadcast has long latency time. In order to overcome the drawback, in this paper, we propose P2Prefix broadcast scheme that can solve the service latency time, which is the problem of broadcast scheme, by using P2P caching as well as minimizing the client buffer requirement.

• KIPS Transactions on Computer and Communication Systems
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• v.12 no.7
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• pp.209-216
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• 2023

Modern HPC systems are equipped with many-core CPUs with dozens of cores. When performing parallel I/O in such a system, there is a limit to scalability due to the problem of the LRU lock management policy of the Linux system. The study proposes an improved FinerLRU to solve this problem. Our new FinerLRU improves the parallel write performance of file systems using the buffer cache through granular lock management by increasing the number of LRU locks upto the maximum number of cores. The proposed method was implemented in Linux 5.18.11, and the performance was measured on two types of CPUs, Intel Icelake Xeon and Intel Knights landing, with different characteristics, and it was found that a performance improvement of about two times can be obtained in both types of systems.