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Application of Self OrganizingMaps for Investigating Network

Latency on Broadcast-basedDistributed Shared Memory

Multiprocessor

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INTRODUCTION

Distributed shared memory(DSM)

multiprocessor, which represent a successful

hybrid of two parallel computer classes :-1. Shared memory multiprocessor

2. Distributed computer systems.

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DSM multiprocessor systems are an

attractive and viable platform for both Parallel

and Mainstream computing.Due to its advantages in terms of

1. Scalability

2. Programmability

3. Cost effectiveness

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Aim of DSM system

To combine of PROGRAMMING of shared

memory multiprocessors with the

SCALABILITY of distributed computersystems.

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DSM system

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Remote Memory Latency

To achieve high performance in DSM

multiprocessor Remote Memory Access time must

be minimized

RML is caused by accessing a memory location in a

processor other than the one originating the request

Network latency is major component of remote

memory latency

Cause most of the time is consumed in

communication over the interconnection network

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Developing methods to minimize the network

latency in broadcast-based optical DSM

multiprocessors requires the knowledge ofthe effect of DSM parameters on the network

latency

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Self-Organizing

Maps

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Overview

Self organizing map (SOM) is a data visualization techniqueinvented by kohonen

SOM is a way to represent higher dimensional data in anusually 2-D or 3-D manner, such that similar data is groupedtogether.

It runs unsupervised and performs the grouping on its own.

SOM is accepted as Analysis tool.

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SOM Structure (kohonen)

Every node is connected to the input the same way, and nonodes are connected to each other.

In a SOM that judges RGB color values and tries to group similar

colors together, each square pixel in the display is a node inthe SOM.

Notice in the converged SOM above that dark blue is near lightblue and dark green is near light green.

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We use SOM to investigate the realtionship

between the network latency and several

DSM parameters on the SimultaneousOptical Multiprocessor Exchange

Bus(SOME-Bus)

SOME-Bus is high bandwidth, optical and

broadcast-based interconnection network

supporting DSM.

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An event based discrete simulator

Is developed for simulating a SOME-Bus

system Which containing 64 nodes,

Each of which has Processor, a Directorycontroller, A cache controller, and an output

channel.

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Node model of DSM-basedSOME-bus system

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State diagram of acb_fifo inOPNET modeler

initarrival

startcomp

l

idle

arrival

arrival

default

default

default

Queue empty

Svc completion

Server busy & insert ok

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Dataset details

Two thousand data points have been collected in order

to create a dataset for study.

Dataset includes 6 parameters

1. Miss rate to a modified block (Pm)2. Fraction of write misses (Pw)

3. Probability of having an upgrade ownership request message

(Puor)

4. Probability of having a cache full (Pcf)

5. Ratio of the mean thread run time to mean message transfer time

(T/R)

6. Network latency

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In observed simulation

Pw ranges from 0.15 to 0.7

Pm takes values varying between 0.2 and0.6

The ration varies between 0.05 and 1

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Let m =miss rate F= number of instruction

per second performed by the processor at

each node, S= mean msg size in bytes andC= channel bandwidth(bytes/s)

Ratio of the mean thread run time to the

mean message transfer time T/R=mSF/C

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CONCLUSION

This paper presents a new application domain

for the use of SOM.

In this paper SOM have been used to

investigate the ralation between network latency

and important DSM parameters

The result shows that network latency has

highest correlation with T/R while Pcf has theleast effect on the values of network latency

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Puor requires high Pw values to

demonstrate strength on network latency

values. Low values of Pw and Pm will yield low

network latencies

Low values of Pw together with high valuesof Pm have a detractive effect on network

latency