엄형상 교수

Ozone (O3) is a flash memory controller that increases the performance of a flash storage system by executing multiple flash operations out of order. In the O3 flash controller, data dependencies are the only ordering constraints on the execution of multiple flash operations. This allows O3 to exploit the multichip parallelism inherent in flash memory much more effectively than interleaving. The O3 controller also provides a prioritized handling of flash operations, equipping flash management so

Fast storage devices are an emerging solution to satisfy data-intensive applications. They provide high transaction rates for DBMS, low response times for Web servers, instant on-demand paging for applications with large memory footprints, and many similar advantages for performance-hungry applications. In spite of the benefits promised by fast hardware, modern operating systems are not yet structured to take advantage of the hardware’s full potential. The software overhead caused by an OS, negl

Large-scale high performance computing (HPC) systems typically consist of many thousands of CPUs and storage units, while used by hundreds to thousands of users at the same time. Applications from these large numbers of users have diverse characteristics, such as varying compute, communication, memory, and I/O intensiveness. A good understanding of the performance characteristics of each user application is important for job scheduling and resource provisioning. Among these performance character

A blockchain wallet is a financial application which provides an interface for managing a digital asset. In the blockchain wallet, a digital signature (single or multiple signatures) is used to sign a transaction. However, the wallet is often vulnerable to security attacks when a single-signature scheme is used, and there are performance issues when a multi-signature scheme is employed. To address these issues, we propose a new efficient multi-signature wallet that improves performance, storage

Native Command Queueing (NCQ) is an optimization technology to maximize throughput by reordering requests inside a disk drive. It has been so successful that NCQ has become the standard in SATA 2 protocol specification, and the great majority of disk vendors have adopted it for their recent disks. However, there is a possibility that the technology may lead to an information gap between the OS and a disk drive. A NCQ-enabled disk tries to optimize throughput without realizing the intention of an

In this paper, we present OS I/O path optimizations for NAND flash solid-state drives, aimed to minimize scheduling delays caused by additional contexts such as interrupt bottom halves and background queue runs. With our optimizations, these contexts are eliminated and merged into hardware interrupts or I/O participating threads without introducing side effects. This was achieved by pipelining fine grained host controller operations with the cooperation of I/O participating threads. To safely ex

Smart CCTV (Closed-Circuit Television) technology has increasingly been developed in the last few years to judge the situation and notify the administrator or take immediate action for security and surveillance reasons. Currently the methods to detect object motion typically include the Frame Difference Method (FDM) which can detect moving objects and the Background Subtraction Method (BSM) which is able to detect motionless objects. Those results can be obtained only if there were some backgrou

Intercloud is a federated environment of private clusters and public clouds. The performance of Hadoop could be degraded significantly in intercloud environments. Because previous solutions for intercloud environments rely on speculative execution, they require additional cost in the cloud. In this paper, we propose a new task scheduler that improves performance without the help of speculative execution in intercloud environments.

This paper presents a family of simulators that have been developed for data-intensive applications, and a methodology to select the most efficient one based on a user-supplied requirement for accuracy. The methodology consists of a series of tests that select an appropriate simulation based on the attributes of the application. In addition, each simulator provides two estimates of application execution time: one for the minimum expected time and the other for the maximum. We present the results

We introduce a new performance metric, called Load Balancing Factor (LBF), to assist programmers with evaluating different tuning alternatives. The LBF metric differs from traditional performance metrics since it is intended to measure the performance implications of a specific tuning alternative rather than quantifying where time is spent in the current version of the program. A second unique aspect of the metric is that it provides guidance about moving work within a distributed or parallel pr

In link-state routing, routes are determined based on estimates of the current delays on the links.Ideally, a data packet should be routed based on the delays it will encounter at each link of the path at the time the packet gets to the link.To address this issue, we have developed a new approach that improves link-state routing by estimating and using the future link delays encountered by data packets.In link-state routing, link-delay estimates are periodically flooded throughout the network.Th

In link-state routing, routes are determined based on the estimates of the current delays on the links, i.e. without considering the dynamics of the link-delay information. Ideally, a data packet should be routed based on the delays it will encounter at each link of the path at the time the packet gets to the link. To address this issue, we have designed a new routing software that improves link-state routing by estimating and using the future link delays encountered by data packets. In link-sta