• Title, Summary, Keyword: Prefetch

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An Active Prefetch Filtering Schemes using Exclusive Prefetch Cache (선인출 전용 캐시를 이용한 적극적 선인출 필터링 기법)

  • Chon Young-Suk;Kim Suk-il;Jeon Joong-nam
    • The KIPS Transactions:PartA
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    • v.12A no.1
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    • pp.41-52
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    • 2005
  • Memory reference instruction caused by cache miss is the critical factor that limits the processing power of processor. Cache prefetching technique is an effective way to reduce the latency due to memory access. However, excessively aggressive prefetch leads to cache pollution and finally to cancel out the advantage of prefetch. In this study, an active prefetch filtering scheme is introduced which dynamically decides whether to commence prefetching after referring a filtering table to reduce the cache pollution due to unnecessary prefetches. For the precision filtering, an evicted address referencing scheme has been proposed where the filter directly compares the current prefetch address with previous unnecessary prefetch addresses stored in filtering table. Moreover, a small sized exclusive prefetch cache has been introduced to increase the amount of eviction of unnecessarily prefetched addresses to enhance the accuracy of dynamic filtering. The exclusive prefetch cache also prevents useful demand data from being pushed out by prefetched data, while the evicted address direct referencing scheme enables the prefetch cache to keep most of useful prefetch data within its small size. Experimental results from commonly used general and multimedia benchmarks show that the average cache miss ratio has been decreased by $13.3{\%}$ by virtue of enhanced filtering accuracy compared with conventional schemes.

Prefetch Method for Multimedia Presentation on Mobile Device (이동 단말기에서 멀티미디어 연출을 위한 버퍼 선일출기법)

  • 공란숙;최원희;박성근;이종호;임영환
    • Proceedings of the Korea Multimedia Society Conference
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    • pp.417-420
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    • 2003
  • 요즘은 여러 멀티미디어 데이터가 기존의 PC에서 재생되는 것이 아니라 핸드폰, PDA와 같은 이동단말기에서 재생되기가 요구되고 있다 멀티미디어 데이터의 용량이 크고 시간에 종속적인 연속 미디어이기 때문에 데이터의 일부론 미리 가져와서 재생하는 Prefetch기법이 필요하다. 영역 분할 기법과 재생가능성 분석기법을 통해서 멀티미디어 프리젠테이션의 재생가능 여부를 분석하고 재생이 불가능한 프리젠테이션은 EPOB지정을 이용한 Prefetch기법을 적용한 후 재생가능 여부를 판단한다. Prefetch하는 시점과 데이터의 양을 지정함으로서 원활한 멀티미디어 프리젠테이션을 재생 할 수 있다.

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The Power and Pitfalls of Data Prefetching (데이터 미리읽기의 동작과 문제점)

  • Ki, An-do
    • Electronics and Telecommunications Trends
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    • v.13 no.4
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    • pp.59-69
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    • 1998
  • The terminology of data prefetching is introduced, which includes stride, repeat distance, stall, pending stall, prefetch degree, prefetch distance, and prefetch offset. The effectiveness of hardware data prefetching in reducing cache misses is shown by presenting a square matrix multiplication example. Thereafter the pitfalls of prefetching and possible solutions are discussed.

An Efficient Instruction Prefetching Scheme Based on the Page Access Information (페이지 접근 정보에 기반한 효율적인 명령어 캐쉬 선인출 기법)

  • Shin Soong-Hyun;Kim Cheol-Hong;Jhon Chu-Shik
    • Journal of KIISE:Computer Systems and Theory
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    • v.33 no.5
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    • pp.306-315
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    • 2006
  • In general, the hit ratio of the first level cache is one of the most important factors in determining the performance of computer systems. Prefetching from lower level memory structure is one of the most useful techniques for improving the hit ratio of the first level cache. In this paper, we propose a prefetch on continuous same page access (CSPA) scheme which improves the prefetch efficiency of the instruction cache and reduces prefetch cost at the same time. The proposed CSPA scheme traces the page addresses of executed instructions to count how many times the same memory page is accessed continuously. To increase the prefetch efficiency, the CSPA scheme initiates prefetch only if the number of accesses to the same page exceeds the threshold value. Generally, the size of a L1 cache block is smaller than that of a L2 cache block. Therefore, one L2 cache block contains a number of L1 cache blocks. To reduce the number of unnecessary accesses to the L2 cache due to prefetch, the CSPA scheme enables prefetch only when the missed L1 block and the prefetch L1 block are in the same L2 cache block, leading to reduced prefetch cost. According to our simulations, the proposed prefetching scheme improves the performance by up to 6.7%.

A Study on the Prefetch Method for Multimedia Presentations to play on the Low Bandwidth Mobile Devices (낮은 대역폭을 갖는 이동 단말기에서 멀티미디어 프리젠테이션을 재생하기 위한 프리패치 방법)

  • Hong Maria;Yang Hyuck;Lim Young-Haw
    • Journal of Internet Computing and Services
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    • v.4 no.4
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    • pp.65-74
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    • 2003
  • Recently, It is required that multimedia data display on not only PC but also the Mobile device such as cellar phone, PDA. Mobile divieces has not sufficient of storage space or main memory and has slow network speed. So we can't process the multimedia data with the existing way on PC. This paper presents various methods for MultimediaPresentation which are able to display on the mobile device with the low-bandwidth and small storage. There Is an analysis that Is playable on the mobile device using presentation area devision method and replayable analysis method. If the display of multimedia presentation is impossible from this analysis, to apply prefetch techniques a using EPOB apoint and as User QoS of multimedia data through prefetch techniques have keep, do so that playable. Then, it is proposed to playable smooth multimedia presentation as that each of the presentations through prefetch Scheduling techniques point and quantity of data which are prefetch.

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Back-end Prefetching Scheme for Improving the Performance of Cluster-based Web Servers (클러스터 웹 서버에서 성능 향상을 위한 노드간 선인출 기법)

  • Park, Seon-Yeong;Park, Do-Hyeon;Lee, Joon-Won;Cho, Jung-Wan
    • Journal of KIISE:Computer Systems and Theory
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    • v.29 no.5
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    • pp.265-273
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    • 2002
  • With the explosive growth of WWW traffic, there is an increasing demand for the high performance Web servers to provide a stable Web service to users. The cluster-based Web server is a solution to core with the heavy access from users, easily scaling the server according to the loads. In the cluster-based Web sewer, a back-end node may not be able to serve some HTTP requests directly because it does not have the requested contents in its main memory. In this case, the back-end node has to retrieve the requested contents from its local disk or other back-end nodes in the cluster. To reduce service latency, we introduce a new prefetch scheme. The back-end nodes predict the next HTTP requests and prefetch the contents of predicted requests before the next requests arrive. We develop three prefetch algorithms bated on some useful information gathered from many clients'HTTP requests. Through trace-driven simulation, the service latency of the prefetch scheme is reduced by 10 ~ 25% as compared with no prefetch scheme. Among the proposed prefetch algorithms, Time and Access Probability-based Prefetch (TAP2) algorithm, which uses the access probability and the inter-reference time of Web object, shows the best performance.

An L1 Cache Prefetching Scheme using Excessively Aggressive Prefetchering and a Small Direct-mapped Filtering Cache (공격적인 선인출 및 직접 사상 필터링을 이용한 L1 캐시 선인출 기법)

  • Chon, Young-Suk
    • Journal of KIISE:Computer Systems and Theory
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    • v.33 no.11
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    • pp.836-852
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    • 2006
  • This paper proposes an L1 cache prefetch scheme using an excessively aggressive hardware prefetcher and a hardware prefetch filter having a small direct-mapped filtering cache. A quantitative analysis method has been introduced and applied to analyze nonideal effects of aggressive cache prefetching. From those analysis results, the structure and algorithm of a prefetch filter has been derived and simulated, and the overall system performance has been measured using a cycle-by-cycle cache simulator. Experimental results show that the proposed scheme improves the overall system performance by 18% on the average over several benchmarks

A Cache Controller to Maximize Effectiveness of Hierarchical Memory Architecture (계층적 메모리 구조의 효과를 극대화하는 캐시 제어기)

  • Uh Bong Yong;Ju Young Kwan;Cheon Joong Nam;Kim Suk Il
    • Journal of KIISE:Computer Systems and Theory
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    • v.32 no.11_12
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    • pp.608-616
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    • 2005
  • A cache architecture is proposed here which evokes prefetch at level 1 cache miss. Existing structures only prefetch at level 2 cache miss. In the proposed cache architecture, level 1 cache miss would select demand fetch block and prefetch block from the level 2 cache and store to level 1 cache and prefetch cache, respectively. According to an experimental analysis using 11 benchmark programs, the hierarchical cache architecture that employs both a level 1 cache prefetcher and a level 2 cache prefetcher obtained a maximum $19\%$ increased performance when compared to the cache architecture that employs only a level 2 cache prefetcher.

Prefetching Mechanism using the User's File Access Pattern Profile in Mobile Computing Environment (이동 컴퓨팅 환경에서 사용자의 FAP 프로파일을 이용한 선인출 메커니즘)

  • Choi, Chang-Ho;Kim, Myung-Il;Kim, Sung-Jo
    • Journal of KIISE:Information Networking
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    • v.27 no.2
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    • pp.138-148
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    • 2000
  • In the mobile computing environment, in order to make copies of important files available when being disconnected the mobile host(client) must store them in its local cache while the connection is maintained. In this paper, we propose the prefetching mechanism for the client to save files which may be accessed in the near future. Our mechanism utilizes analyzer, prefetch-list producer, and prefetch manager. The analyzer records file access patterns of the user in a FAP(File Access Patterns) profile. Using the profile, the prefetch-list producer creates the prefetch-list. The prefetch manager requests a file server to return this list. We set the parameter TRP(Threshold of Reference Probability) to ensure that only reasonably related files can be prefetched. The prefetch-list producer adds the files to a prefetch-list if their reference probability is greater than the TRP. We also use the parameter TACP(Threshold of Access Counter Probability) to reduce the hoarding size required to store a prefetch-list. Finally, we measure the metrics such as the cache hit ratio, the number of files referenced by the client after disconnection and the hoarding size. The simulation results show that the performance of our mechanism is superior to that of the LRU caching mechanism. Our results also show that prefetching with the TACP can reduce the hoard size while maintaining similar performance of prefetching without TACP.

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PMS: Probability-based Multi Successor Prefetch Algorithm for Software Streaming Services of Mobile Embedded Devices (PMS: 모바일 임베디드 시스템의 소프트웨어 스트리밍 서비스를 위한 확률 기반 다중 접근 블록 선인출 알고리즘)

  • Lee, Young-Jae;Park, Seon-Yeong;Pak, Eun-Jj;Lee, Dae-Woo;Jung, Wook;Kim, Jin-Soo
    • Journal of KIISE:Computer Systems and Theory
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    • v.34 no.5_6
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    • pp.238-248
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    • 2007
  • As the demand of employing various PC software on mobile embedded devices which have limited storages has been increased, software streaming services are needed. However it takes too much time to launch software on them because it is transferred through wireless networks. To address this problem, prefetch algorithms are needed. We examined 'Last successor (LS)' algorithm and PPM-based prefetch algorithm as prefetch algorithms for software streaming services. We present 'Probability-base Multi Successor (PMS)' algorithm which is contrived through analyzing evaluations of previous algorithms and characteristics of software streaming services. While LS has one successor per each block, PMS has N successors based on probability which is calculated by PPM-based prefetch algorithm. The hit rate of PMS is similar to that of PPM-base prefetch algorithm and the space overhead is similar to that of LS. We can get good efficiency at the point of memory usage when PMS is applied to software streaming services.