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General-Purpose Computation on Graphics Hardware. Adapted from: David Luebke (University of Virginia) and NVIDIA. Your Presentations. Everyone Must attend 10% loss of presentation points if a day is missed Presentation Grading Criteria posted online Everyone must present

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General purpose computation on graphics hardware

General-Purpose Computation on Graphics Hardware

Adapted from: David Luebke (University of Virginia) and NVIDIA


Your presentations
Your Presentations

  • Everyone Must attend

    • 10% loss of presentation points if a day is missed

  • Presentation Grading Criteria posted online

  • Everyone must present

    • Grades are given to the group, not individual


  • Outline
    Outline

    • Overview / Motivation

    • GPU Architecture Fundamentals

    • GPGPU Programming and Usage

    • New NVIDIA Architectures (FERMI)

    • More Infromation


    Motivation computational power
    Motivation: Computational Power

    • GPUs are fast…

      • 3 GHz Pentium4 theoretical: 6 GFLOPS, 5.96 GB/sec peak

      • GeForceFX 5900 observed: 20 GFLOPS, 25.3 GB/sec peak

      • GeForce 6800 Ultra observed: 53 GFLOPS, 35.2 GB/sec peak

      • GeForce 8800 GTX: estimated at 520 GFLOPS, 86.4 GB/sec peak (reference here)

        • That’s almost 100 times faster than a 3 Ghz Pentium4!

    • GPUs are getting faster, faster

      • CPUs: annual growth  1.5× decade growth  60×

      • GPUs: annual growth > 2.0× decade growth > 1000

    Courtesy Kurt Akeley,Ian Buck & Tim Purcell, GPU Gems (see course notes)


    Motivation computational power1
    Motivation: Computational Power

    GPU

    CPU

    Courtesy Naga Govindaraju


    Motivation computational power2
    Motivation:Computational Power

    multiplies per second

    NVIDIA NV30, 35, 40

    ATI R300, 360, 420

    GFLOPS

    Pentium 4

    July 01

    Jan 02

    July 02

    Jan 03

    July 03

    Jan 04

    Courtesy Ian Buck


    An aside computational power
    An Aside: Computational Power

    • Why are GPUs getting faster so fast?

      • Arithmetic intensity: the specialized nature of GPUs makes it easier to use additional transistors for computation not cache

      • Economics: multi-billion dollar video game market is a pressure cooker that drives innovation


    Motivation flexible and precise
    Motivation: Flexible and precise

    • Modern GPUs are deeply programmable

      • Programmable pixel, vertex, video engines

      • Solidifying high-level language support

    • Modern GPUs support high precision

      • 32 bit floating point throughout the pipeline

      • High enough for many (not all) applications


    Motivation the potential of gpgpu
    Motivation: The Potential of GPGPU

    • The power and flexibility of GPUs makes them an attractive platform for general-purpose computation

    • Example applications range from in-game physics simulation to conventional computational science

    • Goal: make the inexpensive power of the GPU available to developers as a sort of computational coprocessor


    The problem difficult to use
    The Problem: Difficult To Use

    • GPUs designed for and driven by video games

      • Programming model is unusual & tied to computer graphics

      • Programming environment is tightly constrained

    • Underlying architectures are:

      • Inherently parallel

      • Rapidly evolving (even in basic feature set!)

      • Largely secret

    • Can’t simply “port” code written for the CPU!


    Gpu fundamentals the graphics pipeline
    GPU Fundamentals:The Graphics Pipeline

    • A simplified graphics pipeline

      • Note that pipe widths vary

      • Many caches, FIFOs, and so on not shown

    CPU

    GPU

    Graphics State

    Application

    Transform

    Rasterizer

    Shade

    VideoMemory(Textures)

    Vertices(3D)

    Xformed,LitVertices(2D)

    Fragments(pre-pixels)

    Finalpixels(Color, Depth)

    Render-to-texture


    Gpu fundamentals the modern graphics pipeline

    Programmable vertex processor!

    Programmable pixel processor!

    GPU Fundamentals:The Modern Graphics Pipeline

    CPU

    GPU

    Graphics State

    VertexProcessor

    FragmentProcessor

    Application

    VertexProcessor

    Rasterizer

    PixelProcessor

    VideoMemory(Textures)

    Vertices(3D)

    Xformed,LitVertices(2D)

    Fragments(pre-pixels)

    Finalpixels(Color, Depth)

    Render-to-texture


    Gpu pipeline transform
    GPU Pipeline: Transform

    • Vertex Processor (multiple operate in parallel)

      • Transform from “world space” to “image space”

      • Compute per-vertex lighting


    Gpu pipeline rasterizer
    GPU Pipeline: Rasterizer

    • Rasterizer

      • Convert geometric rep. (vertex) to image rep. (fragment)

        • Fragment = image fragment

          • Pixel + associated data: color, depth, stencil, etc.

      • Interpolate per-vertex quantities across pixels


    Gpu pipeline shade
    GPU Pipeline: Shade

    • Fragment Processors (multiple in parallel)

      • Compute a color for each pixel

      • Optionally read colors from textures (images)


    Importance of data parallelism
    Importance of Data Parallelism

    • GPU: Each vertex / fragment is independent

      • Temporary registers are zeroed

      • No static data

      • No read-modify-write buffers

    • Data parallel processing

      • Best for ALU-heavy architectures: GPUs

        • Multiple vertex & pixel pipelines

      • Hide memory latency (with more computation)

    Courtesy of Ian Buck


    Arithmetic intensity
    Arithmetic Intensity

    • Lots of ops per word transferred

    • GPGPU demands high arithmetic intensity for peak performance

      • Ex: solving systems of linear equations

      • Physically-based simulation on lattices

      • All-pairs shortest paths

    Courtesy of Pat Hanrahan


    Data streams kernels
    Data Streams & Kernels

    • Streams

      • Collection of records requiring similar computation

        • Vertex positions, Voxels, FEM cells, etc.

      • Provide data parallelism

    • Kernels

      • Functions applied to each element in stream

        • Transforms, PDE, …

      • No dependencies between stream elements

        • Encourage high arithmetic intensity

    Courtesy of Ian Buck


    Example simulation grid
    Example: Simulation Grid

    • Common GPGPU computation style

      • Textures represent computational grids = streams

    • Many computations map to grids

      • Matrix algebra

      • Image & Volume processing

      • Physical simulation

      • Global Illumination

        • ray tracing, photon mapping, radiosity

    • Non-grid streams can be mapped to grids


    Stream computation
    Stream Computation

    • Grid Simulation algorithm

      • Made up of steps

      • Each step updates entire grid

      • Must complete before next step can begin

    • Grid is a stream, steps are kernels

      • Kernel applied to each stream element


    Scatter vs gather
    Scatter vs. Gather

    • Grid communication

      • Grid cells share information


    Computational resources inventory
    Computational Resources Inventory

    • Programmable parallel processors

      • Vertex & Fragment pipelines

    • Rasterizer

      • Mostly useful for interpolating addresses (texture coordinates) and per-vertex constants

    • Texture unit

      • Read-only memory interface

    • Render to texture

      • Write-only memory interface


    Vertex processor
    Vertex Processor

    • Fully programmable (SIMD / MIMD)

    • Processes 4-vectors (RGBA / XYZW)

    • Capable of scatter but not gather

      • Can change the location of current vertex

      • Cannot read info from other vertices

      • Can only read a small constant memory

    • Future hardware enables gather!

      • Vertex textures


    Fragment processor
    Fragment Processor

    • Fully programmable (SIMD)

    • Processes 4-vectors (RGBA / XYZW)

    • Random access memory read (textures)

    • Capable of gather but not scatter

      • No random access memory writes

      • Output address fixed to a specific pixel

    • Typically more useful than vertex processor

      • More fragment pipelines than vertex pipelines

      • RAM read

      • Direct output


    Cpu gpu analogies
    CPU-GPU Analogies

    • CPU programming is familiar

      • GPU programming is graphics-centric

    • Analogies can aid understanding


    Cpu gpu analogies1
    CPU-GPU Analogies

    CPU GPU

    Stream / Data Array = Texture

    Memory Read = Texture Sample


    Cpu gpu analogies2
    CPU-GPU Analogies

    Loop body / kernel / algorithm step = Fragment Program

    CPU

    GPU


    Feedback
    Feedback

    • Each algorithm step depend on the results of previous steps

    • Each time step depends on the results of the previous time step


    Arb gpu assembly language architecture review board
    ARB GPU Assembly LanguageArchitecture Review Board

    • ABS - absolute value

    • LOG - logarithm base 2 (approximate)

    • MAD - multiply and add

    • MAX - maximum

    • MIN - minimum

    • MOV - move

    • MUL - multiply

    • POW - exponentiate

    • RCP – reciprocal

    • RSQ - reciprocal square root

    • SGE - set on greater than or equal

    • SLT - set on less than

    • SUB - subtract

    • SWZ - extended swizzle

    • XPD - cross product

    • ABS - absolute value

    • ADD - add

    • ARL - address register load

    • DP3 - 3-component dot product

    • DP4 - 4-component dot product

    • DPH - homogeneous dot product

    • DST - distance vector

    • EX2 - exponential base 2

    • EXP - exponential base 2 (approximate)

    • FLR - floor

    • FRC - fraction

    • LG2 - logarithm base 2

    • LIT - compute light coefficients


    Nvidia graphics card architecture

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    IU

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    SP

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    Shared

    Memory

    TEX L1

    TEX L1

    TEX L1

    TEX L1

    TEX L1

    TEX L1

    TEX L1

    TEX L1

    TF

    TF

    TF

    TF

    TF

    TF

    TF

    TF

    L2

    L2

    L2

    L2

    L2

    L2

    Memory

    Memory

    Memory

    Memory

    Memory

    Memory

    Nvidia Graphics Card Architecture

    • GeForce-8 Series

      • 12,288 concurrent threads, hardware managed

      • 128 Thread Processor cores at 1.35 GHz == 518 GFLOPS peak

    Work Distribution

    Host CPU



    Fermi streaming multiprocessor sm
    FERMI: Streaming Multiprocessor (SM)

    • Each SM contains

      • 32 Cores

      • 16 Load/Store units

      • 32,768 registers


    Fermi core architecture
    FERMI: Core Architecture

    • Newer FP representation

      • IEEE 754-2008

    • Two units

      • Floating point

      • Integer

    • Simultaneous execution possible






    Applications
    Applications

    • Includes lots of sample applications

      • Ray-tracer

      • FFT

      • Image segmentation

      • Linear algebra


    Brook performance
    Brook performance

    2-3x faster than CPU implementation

    ATI Radeon 9800 XT

    NVIDIA GeForce 6800

    • GPUs still lose against SSE

    • cache friendly code.

    • Super-optimizations

      • ATLAS

      • FFTW

    • compared against 3GHz P4:

    • Intel Math Library

    • FFTW

    • Custom cached-blocked

    • segment C code


    Gpgpu examples
    GPGPU Examples

    • Fluids

    • Reaction/Diffusion

    • Multigrid

    • Tone mapping


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