workshop on commodity-based visualization clusters integration of a commodity cluster into an...

Workshop on Commodity-Based Visualization Clusters

Integration of a Commodity Cluster into an Existing 4-Wall Display System

Douglas B. Maxwell, Aaron Bryden, Greg S. Schmidt, Ian Roth, Sue-Ling Chen

Virtual Reality Laboratory, Naval Research Laboratory

2Workshop on Commodity-Based Visualization Clusters

General Overview

Introduction

Project Rationale

Related Work

System Overview Cluster Design Strategies Graphics Cluster Requirements NRL VR-Lab Hardware Overview

System Implementation Software Physical Installation

Testing and Evaluation

Summary and Conclusions


Introduction

Not all virtual reality applications today require the power or expense of single large visualization “supercomputers”.

Increasingly, low cost commodity consumer electronics and computing technology are becoming powerful enough to present an acceptable level of graphics performance.

Already, commodity PCs are driving virtual reality workbenches with stereo and tracking options.


Project Rationale

Why should anyone use a commodity cluster when the capability already exists with solutions from SGI and Sun?

Rapid evolution of commodity computers and consumer electronics has both driven down costs and accelerated obsolescent computing cycles.

A general rule to follow for buying graphics capability from SGI is to budget $250,000 per graphics pipe.

Our experimental cluster costs less than $1000 per node.


Project Rationale

We present an experiment that integrates a commodity cluster into an existing 4-wall display system—a Surround-Screen Visualization System (SSVR) from Mechdyne Corporation.

The objective is to attain active stereo visualization on multiple walls using genlocking, swap-locking and data-locking capabilities – all with acceptable stereo frame rates.

The cluster was designed from the beginning to attempt to replace aging SGI computing equipment used to drive our current 4-wall display system.


Related Work

Siggraph 2002 - Course Notes 47 ”Commodity Clusters for Immersive Projection Environments”

Cornell Theory Center Deploys the First Ever Immersive Display Using the Windows 2000 Cluster CAVELib™

http://noel.feld.cvut.cz/magi/

Net Juggler - The Scalable High Performance Virtual Reality Project http://netjuggler.sourceforge.net


System Overview

Cluster Design Strategies Client/Server Master/Slave

Graphics Cluster Requirements Genlocking Swap Locking Data Locking

NRL VR-Lab Hardware Overview


Cluster Design Strategies

Client/Server

Consists of a single node of a cluster serving data to the graphics rendering clients.

Advantages: Many applications may embed

a server that works with the same rendering client nodes.

Flexible

Disadvantage: High network bandwidth

consumption.

Master/Slave

Consists of multiple nodes, where each node of the cluster locally stores and runs an identical copy of the application.

Advantages: Small amounts of data is

transferred; Network bandwidth is less of a concern.

Disadvantage: Inflexible


Graphics Cluster Requirements

Genlocking is the process of synchronizing the video frames from each node in a graphics cluster so that they produce a fluid, coherent image.

Swap Locking is the process of synchronizing the frame buffer rendering and swapping.

Data Locking is the process of synchronizing the views to maintain consistency across all screens.



3 node cluster graphics cluster in master/slave configuration using commodity PC’s.

Generic PC configuration: AMD Duron Processors @ 1.2Ghz 512 Mb ram NVidia GeForce 4 Ti4600 w/ 128 Mb video memory

Networking: 10/100 NICs 100BaseT Switch



Video Insertion of video output from cluster into existing 4-wall

display achieved by an Extron CrossPoint 124 matrix video switcher.

Misc. Genlocking and data locking are handled in software

through the parallel ports. A special purpose communication box was fabricated

from COTS hardware. This box also outputs a genlocking signal to a set of Crystal Eyes infrared emitters.



Commodity Cluster Configuration Diagram


System Implementation - Software

Software used to deal with active stereo and scene synchronization needs of the graphics cluster:

Real Time Application Interface (RTAI) kernel patch applied to Red Hat 7.2. RTAI allows for low latency and task completion timing.

SoftGenLock enables active stereo in clusters.

SoftGenLock and RTAI are used in concert to provide a software active stereo solution.


RTAI Kernel Module - Active Stereo

The RTAI kernel module detects the vertical refresh and changes a pointer in the video card memory.

Simulated Frame Buffer Contents


System Implementation – Software

Genlock/data lock is achieved by synchronizing the machines through the parallel ports.

The RTAI kernel module reads and writes to two pins on the parallel port.

The master tells all the other nodes in the cluster when to draw.

Parallel Port Signal Adapter


System Implementation – Software

SoftGenLock does not synchronize applications between the nodes of a cluster; It provides data lock and stereo only.

It is the responsibility of the application to synchronize the viewing frustum and animations in the application.

SoftGenLock only uses VGA registers, it potentially can work with any graphics card.


Physical Installation – Setup Issues for Consideration

Adequate HVAC, power and network access where the cluster will be set up.

Set up the cluster and display system in separate rooms, since noise levels from fans, drives, etc. may be distracting.

Prepare to deal with a lot of issues associated with cables.

Create a master power switch to turn off all units at once.


Testing and Evaluation

Commercial Software

Software Design


Commercial Software

VR Juggler– Open source virtual reality tools (LGPL)– VR interoperable

• Works on multiple computing platforms• Works with multiple display systems• Works with multiple tracking and interaction devices

– Works with advanced 3D visualization tools• Open GL• Open Scene Graph library• SGI OpenGL Performer

– Free Software (LPGL)– www.vrjuggler.org

Open GL


Software Design

VBU Software Displays bathymetry and has capability to load simple models Utilizes VR Juggler, OpenGL Works on SGI and Linux platforms Works with standard 4-wall CAVE, workbench, desktop

VBU Software on Linux Desktop Bathymetry Uncertainty Using Glyphs


Software Design

VBU Software Adapted to work with pc-cluster (3 machines) Works on 3 walls of CAVE

3-PC Cluster Running VBU Software

VBU Software Running on 3 Walls of CAVE Driven by 3-PC Cluster


Summary and Conclusions

The use of a graphics PC cluster is now becoming a viable low-cost alternative to the use of single large visualization supercomputers.

Our cluster experiment explored the feasibility of phasing out and replacing existing expensive single large computing hardware.

The results show we can make this kind of transition in the near future, and we believe our experiences will be motivation for others to follow suit.


Contact Information

Douglas B Maxwell, MSME

Advanced Systems Division

Weapon Countermeasure Control Branch

Naval Undersea Warfare Center

[email protected]

Gregory Schmidt, Ph.D.

Virtual Reality Laboratory

Naval Research Laboratory

[email protected]


Acknowledgement

Thanks are extended to Dr. Larry Rosenblum for the resources and support necessary to make this project a success.

workshop on commodity-based visualization clusters integration of a commodity cluster into an...

Documents

commodity clusters

commodity pcs

cluster cavelib http

experimental cluster

active stereo visualization

graphics capability

wall display system

graphics pipe