• Journal of KIISE:Computer Systems and Theory
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• v.30 no.1
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• pp.33-49
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• 2003

Recently, there have been large storage demands for manipulating multimedia data. To solve the tremendous storage demands, one of the major researches is the SAN(Storage Area Network) that provides the local file requests directly from shared-disk storage and also eliminates the server bottlenecks to performance and availability. SAN also improve the network latency and bandwidth through new channel interface like FC(Fibre Channel). But to manipulate the efficient storage network like SAN, traditional local file system and distributed file system are not adaptable and also are lack of researches in terms of a metadata structure for large-scale inode object such as file and directory. In this paper, we describe the architecture and design issues of our shared-disk file system and provide the efficient bitmap for providing the well-formed block allocation in each host, extent-based semi flat structure for storing large-scale file data, and two-phase directory structure of using Extendible Hashing. Also we describe a detailed algorithm for implementing the file system's device driver in Linux Kernel and compare our file system with the general file system like EXT2 and shard disk file system like GFS in terms of file creation, directory creation and I/O rate.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.9
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• pp.459-466
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• 2007

TCP/IP processing imposes a heavy load on the host CPU when it is processed by the host CPU on a very high-speed network. Recently the TCP/IP Offload Engine (TOE), which processes TCP/IP on a network adapter instead of the host CPU, has become an attractive solution to reduce the load in the host CPU. There have been two approaches to implement TOE. One is the software TOE in which TCP/IP is processed by an embedded processor and the other is the hardware TOE in which TCP/IP is processed by a dedicated ASIC. The software TOE has poor performance and the hardware TOE is neither flexible nor expandable enough to add new features. In this paper we designed and implemented a hybrid TOE architecture, in which TCP/IP is processed by cooperation of hardware and software, based on an FPGA that has two embedded processor cores. The hybrid TOE can have high performance by processing time-critical operations such as making and processing data packets in hardware. The software based on the embedded Linux performs operations that are not time-critical such as connection establishment, flow control and congestions, thus the hybrid TOE can have enough flexibility and expandability. To improve the performance of the hybrid TOE, we developed a hardware-based transmission/reception accelerator that processes important operations such as creating data packets. In the experiments the hybrid TOE shows the minimum latency of about $19{\mu}s$. The CPU utilization of the hybrid TOE is below 6 % and the maximum bandwidth of the hybrid TOE is about 675 Mbps.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.1
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• pp.26-32
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• 2009

The multi-level storage architecture has been widely adopted in servers and data centers. However, while prefetching has been shown as a crucial technique to exploit sequentiality in accesses common for such systems and hide the increasing relative cost of disk I/O, existing multi-level storage studies have focused mostly on cache replacement strategies. In this paper, we show that prefetching algorithms designed for single-level systems may have their limitations magnified when applied to multi-level systems. Overly conservative prefetching will not be able to effectively use the lower-level cache space, while overly aggressive prefetching will be compounded across levels and generate large amounts of wasted prefetch. We design and implement a hierarchy-aware lower-level prefetching strategy called PMS(Prefetching strategy for Multi-level Storage system) that applicable to any upper level prefetching algorithms. PMS does not require any application hints, a priori knowledge from the application or modification to the va interface. Instead, it monitors the upper-level access patterns as well as the lower-level cache status, and dynamically adjusts the aggressiveness of the lower-level prefetching activities. We evaluated the PMS through extensive simulation studies using a verified multi-level storage simulator, an accurate disk simulator, and access traces with different access patterns. Our results indicate that PMS dynamically controls aggressiveness of lower-level prefetching in reaction to multiple system and workload parameters, improving the overall system performance in all 32 test cases. Working with four well-known existing prefetching algorithms adopted in real systems, PMS obtains an improvement of up to 35% for the average request response time, with an average improvement of 16.56% over all cases.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.2
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• pp.66-75
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• 2010

This paper proposes an efficient method for design and implementation of the artificial intelligence (AI) of 'omok' game on the GPU. The proposed AI is designed on a cooperative structure using min-max game tree and genetic algorithm. Since the evaluation function needs intensive computation but is independently performed on a lot of candidates in the solution space, it is computed on the GPU in a massive parallel way. The implementation on NVIDIA CUDA and the experimental results show that it outperforms significantly over the CPU, in which parallel game tree and genetic algorithm on the GPU runs more than 400 times and 300 times faster than on the CPU. In the proposed cooperative AI, selective search using genetic algorithm is performed subsequently after the full search using game tree to search the solution space more efficiently as well as to avoid the thread overflow. Experimental results show that the proposed algorithm enhances the AI significantly and makes it run within the time limit given by the game's rule.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.1
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• pp.18-29
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• 2008

NAND Flash memory has been growing popular storage device for the last years because of its low power consumption, fast access speed, shock resistance and light weight properties. However, it has the distinct characteristics such as erase-before-write architecture, asymmetric read/write/erase speed, and the limitation on the number of erasure per block. Due to these limitations, various Flash Translation Layers (FTLs) have been proposed to effectively use NAND flash memory. The systems that adopted the conventional FTL may result in severe performance degradation by the hot data which are frequently requested data for overwrite in the same logical address. In this paper, we propose a novel FTL algorithm called Adaptive Flash Translation Layer (AFTL) which uses sector mapping method for hot data and log-based block mapping method for cold data. Our system removes the redundant write operations and the erase operations by the separating hot data from cold data. Moreover, the read performance is enhanced according to sector translation that tends to use a few read operations. A series of experiments was organized to inspect the performance of the proposed method, and they show very impressive results.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.11
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• pp.626-634
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• 2004

In a client-server model, network server systems suffer from both heavy communication and computational loads. While communication channels become increasingly speedy, the existing protocol stack architectures still include mainly three performance bottlenecks of protocol stack processing, system call, and network interrupt overheads. To address these obstacles, in this paper we present a host-independent network system where a network interface card (NIC) is utilized in an efficient manner. First, by offloading network-related portion to the NIC, the host can fully utilize its processing power for other useful purposes. Second, it eliminates the system call overhead, such as context-switching and memory copy operations, since the host communicates with the NIC through its user-level libraries. Third, it a] so reduces the network interrupt operation count as the host handles the interrupt in a segment instead of a packet. The experimental results show that the proposed network system reduces the host CPU overhead for communication system by 68-71%. It also shows that the proposed system improves the communication speed by 11-83% under heavy computational and communication load conditions.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.11_12
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• pp.663-674
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• 2005

We propose a system aimed at achieving high energy-delay efficiency by using adaptive victim caches. Particularly, we investigate methods to improve the hit rates in the first level of memory hierarchy, which reduces the number of accesses to mort power consuming memory structures such as L2 cache. Victim cache is a memory element for reducing conflict misses in a direct-mapped L1 cache. We present two techniques to fill the victim cache with the blocks that have higher probability to be re-reqeusted by processor. Hit-based victim cache ks tilled with the blocks which were referenced frequently by processor. Replacement-based victim cache is filled with the blocks which were evicted from the sets where block replacements had happened frequently According to our simulations, replacement-based victim cache scheme outperforms the conventional victim cache scheme about $2\%$ on average and refutes the power consumption by up to $8\%$.

• Korean Journal of Heritage: History & Science
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• v.50 no.2
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• pp.62-79
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• 2017

The principle of repairing the architectural heritage in China was first presented by Liangsicheng of Society for Research in Chinese Architecture in the 1930s, and it was stated as "Restoration of Historic Condition or Preservation of Existing Condition" in 1961 in the "Provisional Regulations on the Protection and Management of Cultural Relics" after various repair experiences under the social and political background of the 1950s. Restoration of historic condition generally means restoration to original shape, and because architectural heritage was often repaired based on similar principle in Korea and Japan in the early and mid 20th century, it can be said that the restoration of historic condition was a universal and leading principle in this period in Northeast Asia. In China, however, the preservation of existing condition is equally specified along with the restoration of historic condition. When considering the leading trend of the time, it seems to be rather unexpected, which leads to questions about the formation process and meaning. The research on Liangsicheng, which first suggested the principle of repair, is very important, but there is a lack of three-dimensional analysis of his principles compared with active research on international principles in China. In order to understand the process of formation and its meaning of the principle of repair in China, we first need to analyze the principle proposed by Liangsicheng, and it is necessary to comprehensively examine how the principle have changed under the social background surrounding architectural heritage conservation after the founding of the People's Republic of China(PRC). In this paper, we first show that Liangsicheng has proposed a principle of restoration of historic condition with important values in the originality, and at the same time he opened the possibility of preservation of existing condition for the result of value judgment or realistic reason. In addition, we examine the process of equalizing preservation of existing condition with a restoration of historic condition as a realistic principle due to the influence of Soviet architectural heritage conservation system and Chinese economic development oriented policy after the founding of PRC.

• Journal of the Korean Institute of Landscape Architecture
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• v.51 no.2
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• pp.94-102
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• 2023

The Florence Charter, established in 1981 by the ICOMOS-IFLA International Commission on Historic Gardens, considered the historic garden as a plant-dominated architectural composition, a perpetual balance between the artist and the artisan's desire to remain unaltered in perpetuity. Trees, the main component of the garden, require continuous management as they repeat their creation and calling according to the cycle of the seasons and accordingly, it is suggested that management to maintain the appearance of trees in Korean palaces was an indispensable element. Although it is an important matter to historically verify the tree management techniques of the palaces of the past, research has been difficult due to the absence of historical records and the disconnection of life due to the Japanese colonial period. In addition, according to the view that trees were not generally managed in the palace, research on palace tree management techniques has not been conducted so far. Therefore, this study aimed to examine whether or not the tree management of the palaces was performed in the past through expert interviews based on photographs taken in modern times. With the identification of tree species and pruning through in-depth interviews with experts using photographs taken in the modern period, the results are as follows. First, it was found that the shapes of trees and leaves could be identified through photographs and by observing the phenomena caused by planting and pruning, it was possible to estimate whether or not the tree management was implemented in the modern palace. Second, as a result of in-depth interviews with 8 experts in 4 fields, it was possible to determine the tree species and pruning status, purpose, and method. There was no significant difference in opinions between groups, and the evidence was clearly presented. Third, the type of management of trees in the palace was mainly found to be determination of the types of tree, removal of hazardous factors of trees, and management of lower vegetation and through the photographs of Jondeokjeong and Gwanwanjeong, it was confirmed that the trees were managed even before the Japanese colonial era, considering the time of filming. Based on the photographs taken, it was possible to estimate whether the trees were managed before the Japanese colonial period through expert interviews. However, it could not be clarified due to lack of historical materials as to whether it was carried out on its own according to the circumstances of the times or by the Japanese Empire. Still, in this study, evidence was obtained to refute the view that trees of the palace were not managed in the past through the collected data. Expert opinions supporting this view were collected to make the conclusion. In addition, based on the general theory of pruning, an empirical review of expert opinions was conducted to secure the reliability of the research results.

• Journal of the Korean Institute of Landscape Architecture
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• v.50 no.2
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• pp.64-75
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• 2022

The purpose of this study is to illuminate the meaning of the soundscapes of two bells, Daeheung-dong Cathedral and Sungsimdang in Eunghang-dong, which are landmarks and attractions in the historic downtown of Daejeon. The study was conducted through field research and recordings, as well as literature studies of related documents and soundscape theory. Daejeon city was developed along with Daejeon Railway Station during the Japanese colonial period in the early 20th century. As the Chungnam Provincial Office moved to Daejeon, Daeheung-dong and Eunhang-dong in Jung-gu, located near Daejeon Station, developed significantly and formed the city centre. As major administrative agencies moved to Seo-gu in the 1990s, the downtown area of Daejeon was on a path of decline, and the decline accelerated with the development of Sejong city. Meanwhile, Daeheung-dong Cathedral and Sungsimdang, founded by refugees during the Korean War, firmly protected the historic downtown area of Daejeon, where the natives left. Daeheung-dong Cathedral, established during the Japanese colonial period, is a local landmark with a history of 100 years in 2019. Sungsimdang, which was created with the backdrop of the Korean War, is also a historical and cultural asset with a history of 60 years and a local landmark selected as the No. 1 tourist attraction in Daejeon. This research, which started from the sound of the bells of Daeheung-dong Cathedral, heard even in the neighboring residential areas, led to the discovery of the bells of Sungsimdang in Eunhang-dong, located across the street. In this paper, the bells of Daeheung-dong Cathedral and Eunhang-dong Sungsimdang have characteristics of soundmarks according to R. Murray Schafer's soundscape sound category. Furthermore, this paper attempted to analyze the meaning of the two bells according to the relatively recent EU soundscape definition. These two bells are signal sounds at the surface level, but are the sound marks of the historic downtown area of Daejeon at the deep level. Although there are outward differences in size, scale, frequency, and famousness, these two bells share a meaning in terms of locality and good influence with the historicity and spatiality of a special relationship. The implication of this study is that the two places should be preserved as local historical and cultural assets not only as visual landmarks but also as sound marks in the urban regeneration or urban development of Jung-gu, Daejeon.