在最近這幾年中，叢集計算已經成為可以節省成本的計算方法。因為它集合了資源的計算的能力、通訊以及儲存的空間。它同時也被認為是最吸引人的低成本之超級計算平台。分散式共享記憶體提供了方便而且有效率的方法讓程式在Linux叢集式系統上平行化的執行。
在分散式共享記憶體中，由於是使用各台電腦的實體記憶體去形成一個廣域的共享的記憶體，因此共享記憶體是分散在各台電腦上，所以當要存取資料時，便會經常需要到遠端的電腦上去存取所要用到的資料。因此，它造成了遠端存取的效能延遲，這也正是分散式共享記憶體系統負擔的主要因素。現在有許多策略可以用來改善這個問題。而在這些策略當中，先取策略可以有不錯的效能。先取策略可以藉由先取的動作以達到減少遠端存取的延遲進而達到改善這些現象。但是，它卻也增加了擁有頁擁有權的電腦的工作量。而且，在做先取的動作時，其他的電腦必須等待擁有頁擁有權的電腦去傳送先取策略的資料，若是擁有頁擁有權的電腦得傳送先取策略的資料給許多電腦的話，其他電腦將會花費許多時間在等待擁有頁擁有權的電腦上。
因此我們提出一個方法用以減少擁有頁擁有權的電腦的負擔，它是藉由暫時提供一個代理主機去分擔擁有頁擁有權的電腦的工作量，讓擁有頁擁有權的電腦在傳送先取策略的資料時，能夠把工作量分散給其他的電腦，讓其他的電腦能夠代為傳送先取策略的資料。透過這樣的方式可以降低擁有頁擁有權的電腦的工作負擔，達到平衡各台電腦的工作量，以減少等待的時間。

In recent years, the cluster computing technology has become a cost-effective computing infrastructure, because it aggregates resources of computational power, communication and storage. It is also considered a very attractive platform for low-cost supercomputing. Software distributed shared memory（DSM）provides a convenient and effective solution for programming parallel applications on Linux-based Cluster systems.
In distributed shared memory（DSM）systems, it uses physical memories of each computer to form a global shared memory. Otherwise, shared memory is distributed on each computer so it is the common need to access data in remote nodes. Thus, it induces remote access latencies, what is the major factor of overhead for DSM systems. There are many strategies can improve this problem. Prefetching strategies can improve these phenomena by reducing latencies, but it adds workload to home nodes. When proceeding prefetching, other nodes need to wait home node to transfer prefetching data. If home node needs to transfer prefetching data to many nodes, other nodes will spend a lot of time on waiting home node.
We propose a method to reduce overhead of home nodes, by providing an agent home to share the workload of home nodes, by distributing these workloads to other nodes when sending data. That let other nodes can transfer prefetching data for home node. By this way, we can reduce workload of home node, achieve balancing workload of each node, and reduce waiting time.

Chinese Abstract i
English Abstract ii
Acknowledgement iii
Contents iv
List of Tables vi
List of Figures vii

Chapter 1 Introduction..................................................1
1.1 Overview..............................................................2
1.2 Motivation............................................................4
1.3 Objective.............................................................5
1.4 Organization..........................................................6
Chapter 2 Related Work..................................................7
2.1 Related Consistency Models........................................... 8
2.2 Home-based and Homeless Protocol.....................................11
2.3 Adaptive Home-Based Lazy Release Consistency.........................13
2.4 Prefetching Strategies...............................................15
2.4.1 History Prefetching Strategy.......................................16
2.4.2 Aggregate Prefetching Strategy.....................................17
2.4.3 Effective Prefetching Strategy .................. ......... ......... 19
2.5 Comparisons between Our Agent Home Strategy and Other Methods........ 21
Chapter 3 Agent Home Strategy.......................................... 22
3.1 Overview.............................................................22
3.2 Agent Home of Prefetching Strategy...................................24
3.2.1 Concept............................................................ 24
3.2.2 Method............................................................. 26
Chapter 4 Implementation...............................................29
4.1 Memory Organization of JIAJIA........................................29
4.2 System Architecture of JIAJIA........................................30
Chapter 5 Performance Evaluation....................................... 32
5.1 Execution Time .......................................................33
5.2 SEGV Time............................................................35
5.3 Barrier Time.........................................................37
5.4 Communication Time...................................................39
5.5 Transport Message Count..............................................41
Chapter 6 Conclusions and Future Work..................................45
6.1 Conclusion........................................................... 45
6.2 Future Work.......................................................... 45
Reference ................................................................47
Vita.....................................................................51

Appendic A 3DFFT code..................................................52
Appendix B Red-Black SOR code..........................................66
Appendix C IS code.....................................................69
Appendix D LU code.....................................................74

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