Design%20Issues%20of%20Prefetching%20Strategies%20for%20Heterogeneous%20Software%20DSM

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Design Issues of Prefetching Strategies for
Heterogeneous Software DSM

• Author Ssu-Hsuan Lu, Chien-Lung Chou,
  Kuang-Jui Wang, Hsiao-Hsi Wang, and
  Kuan-Ching Li
• Speaker Chien-Lung Chou
• Date 2006/05/18

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Outline

• Introduction
• Motivation
• Related Work
• Proposed Method
• Performance Evaluation
• Conclusions and Future Work

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Introduction

• In Distributed Shared Memory (DSM) systems, it
  induces
• large number of page faults.
• large number of communication time.

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Introduction (cont.)

• Page faults and communication time are major
  overheads in DSM systems.
• We need additional strategies to reduce page
  faults and communication time are
• Home migration
• Write vector
• Prefetching

5
Introduction (cont.)

• Most traditional prefetching strategies can
  provide good performance in homogeneous cluster
  platforms.
• However, the performance of such strategies may
  be worse in heterogeneous environment.

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Motivation

• Homogeneous cluster platform.

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Motivation (cont.)

• Heterogeneous cluster platform

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Motivation (cont.)

• We need to concern about heterogeneous
  environment.
• More and more personal computers will be perform
  computations collectively.
• Large number of advanced techniques will be
  develop in this environment.
• We will usually meet this environment in future.

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Related Work

• History Prefetching Strategy.
• It permits home nodes sending data to remote
  nodes in advance.
• It has some disadvantages
• Accumulated Waiting Phenomenon.
• Waiting Synchronization Phenomenon.
• Misprefetch.
• Home nodes have too much work.

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Related Work (cont.)

• Effective Prefetch Strategy
• Filtering Unnecessary Prefetches.
• Distributing Prefetch Overhead.
• Load Balancing with Barrier Synchronization.
• Agent Home of prefetching strategy
• It will find a node that will help home nodes to
  transfer prefetching data.
• Thus, it reduces overhead of home nodes.

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Proposed Method
Prefetching Strategy in Heterogeneous
Environments
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Proposed Method (cont.)

• According to above disadvantages, we propose the
  method that allows
• home nodes are adjusted to suitable place.
• high speed processors to execute prefetch in
  advance.
• low speed processors to leave the barrier early.

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Proposed Method (cont.)

• First, we distribute home pages to nodes that
  have better resources.
• These nodes are suitable to be home nodes because
  they have better performance.

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Proposed Method (cont.)

• Second, we observe that hosts that have worse
  resources finish work later, so we adjust policy
  of prefetching strategy.
• Originally, all hosts leave barrier at the same
  time.

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Proposed Method (cont.)

• In our method, the hosts that have worse
  resources leave barrier after requesting
  prefetching data.
• The hosts that have better resources leave
  barrier after sending prefetching pages to hosts
  that have worse resources.

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Proposed Method (cont.)

• Third, we also observe that hosts that have
  better resources spend large amount of idle time
  during barrier in heterogeneous environment.
• It raises execution time and barrier time.

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Proposed Method (cont.)

• We utilize idle time in barrier of hosts that
  have better resources to perform prefetching to
  each other.

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Proposed Method (cont.)

• Our Proposed Method

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Performance Evaluation

• Experimental Platform - Hardware

Node ID CPU Memory Network
1 Intel P4 2.4GHz 256MB Fast Ethernet
2 Intel P4 1.7GHz 256MB Fast Ethernet
3 Intel P3 500MHz 640MB Fast Ethernet
4 Intel P2 350MHz 128MB Fast Ethernet
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Performance Evaluation (cont.)

• Experimental Platform - Software
• Linux Fedora Core 3.
• Kernel 2.6.9.
• JIAJIA DSM software.

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Performance Evaluation (cont.)
Host 1 Host 2 Host 3 Host 4
Idle Time in Barrier JIAJIA 70.71 67.79 27.00 0.36
Idle Time in Barrier History Prefetch 72.72 71.05 30.45 0.78
Idle Time in Barrier Effective Prefetch 68.31 67.42 26.60 0.63
Idle Time in Barrier Agent Home 70.72 68.61 28.11 0.63
Idle Time in Barrier Our Method 62.14 62.16 26.77 0.56
The Idle Time in Barrier for IS Application
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Performance Evaluation (cont.)
Host 1 Host 2 Host 3 Host 4
Idle Time in Barrier JIAJIA 3.75 7.35 8.67 8.21
Idle Time in Barrier History Prefetch 3.83 6.25 7.49 7.02
Idle Time in Barrier Effective Prefetch 3.92 6.29 7.43 6.97
Idle Time in Barrier Agent Home 4.34 6.03 7.03 6.57
Idle Time in Barrier Our Method 2.37 2.38 4.91 4.35
The Idle Time in Barrier for Merge
Application
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Performance Evaluation (cont.)

• Performance Benefits

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Conclusions and Future Work

• In heterogeneous environment, benefits of
  original prefetching strategies are limited.
• In this paper, we utilized idle time to improve
  overall performance.
• In the best situation, our proposed method could
  reduce idle time in barrier of about 60.

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Conclusions and Future Work (cont.)

• In the future, we will make effort to find a
  method to optimize the use of idle time in
  barrier.
• In addition, we will also investigate the
  parallel program execution with issues about
  dynamic CPU loads include in our next development
  stage.

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• Thank You!!