Semester B Presentation

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Semester B Presentation

• CityWall

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Objectives

• Build a display wall system
• Use PC cluster Abacus
• Features
• Low cost
• High efficiency

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4 Phases

• 1. Upgrade display wall system (X window)
• 2. Search library and decoder
• 3. Develop a parallel model
• 4. Build a parallel MPEG player

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Summary of Sem A

• Re-constructure Abacus
• Setting
• NFS (Network File System)
• NIS (Network Information Service)
• LAM/MPI 6.3.2 / 6.5.4
• X window
• Search library and decoder

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Summary of Sem Break

• Build the Parallel Display Model (Bouncing Ball)
• With SDL (Simple DirectMedia Layer)
• With SMPEG (SDL MPEG Player Library)
• Start reading the player source code
• Documentation

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Background

• X window system
• Client-Server mode display system
• X server (display)
• X client (application)

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Background 2

• SDL
• Cross-platform multimedia library (Linux, Win32,
  BeOS, MacOS, Solaris, IRIX, and FreeBSD)
• Fast access to the graphics framebuffer and audio
  device
• Used by MPEG playback software
• Written in C
• Has bindings to Ada, Perl, PHP, etc.

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Background 3

• SMPEG
• Open source project of Loki Software
• A general purpose MPEG video/audio player
• Base on SDL
• SDL extension library

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Background 4

• MPI
• Common parallel computing technique
• Send
• MPI_SEND(buf, count, datatype, dest, tag, comm)
• Receive
• MPI_RECV (buf, count, datatype, source, tag,
  comm, status)
• Blocking
• MPI_BARRIER( comm )
• Broadcast
• MPI_BCAST( buffer, count, datatype, root, comm )

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Implementation - X window

• X Server
• server serves displaying capabilities to other
  programs that connect to it
• e.g. xhost abacus.ee.cityu.edu.hk
• X Client
• know which display to connect to by inspecting
  the DISPLAY environment variable
• e.g. DISPLAYlocalhost4

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Implementation - X window (2)

• Telnet system
• Pseudo terminal, no display
• How to display on remote screen?
• How to login a X session?
• Root (insecure)
• Non-privileged user automatic login
• Ximian
• XDMCP (X Display Manager Control Protocol)

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Implementation - SDL

• Locus of Bouncing Ball
• Incident angle Reflection angle

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current
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Implementation SDL (2)

• Local model
• Avoid synchronization and communication
• Draw the ball with Flash
• Import into a surface with SDL
• Video mode
• best pixel format
• SDL_SWSURFACE
• SDL_HWSURFACE
• SDL_FULLSCREEN

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Implementation SDL (3)

• Image border
• Frame counter
• Regional update

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Implementation SDL (4)

• Parallel model
• 4 problems
• Connect a remote node and own it's X display
• DISPLAY parameter
• Login script (.bash_profile)
• RSH documents
• MPI (-x DISPLAY)

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Implementation SDL (5)

• Split up original frame to 9 parts according to
  their nodes' position
• Identify nodes rank
• Need one more surface
• Synchronize the frame number of each node
• MPI_BARRIER(comm)
• Make all events occurring in server node able to
  be passed to all other nodes
• MPI_BCAST( buffer, count, datatype, root, comm )

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Ways of MPEG Player (1)

• Run the MPEG player (X client) locally, but
  connect to the remote X server
• Simplest method
• Server node needs to run 9 decoders and thread 9
  players on 9 screens at the same time
• Does not utilize the computational power of other
  nodes

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Ways of MPEG Player (2)

• 9 decoders and players running on different nodes
  
• Server node plays the role of a middle-man to
  handle communication
• Each node decodes their own copy of video
• Bandwidth bottleneck

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Ways of MPEG Player (3)

• Other ways
• Run a single decoder locally and threads 9
  players to other nodes
• Transmit part of the frame data to the
  corresponding node to relief the traffic
• Need a special decoder
• We want a good parallel model rather than a
  robust decoder

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The End of Presentation

• Q A