this presentation covers some general topics about current GPU architecture, how one can use it, how one can code on this...

1. Bartłomiej Filipek
www.bfilipek.com
mail@bfilipek.com

2.  How does this work?
 General architecture
 Advices
 Tools
The lecture will not cover the
technical details about the gpu, it
shows only overview needed to
understand current technologies
and standads.

3. GPU
CPU
Vertex Fragment
Processing Processing
application
BUS
Commands, Textures, Framebuffer
3D Api Vertices, Shaders,
(DirectX/OpenGL)
Data… Memory
Driver
Display

4. Vertex units
Vertex
Processing
Memory/textures
Fragment
Processing
As we can see, previous architectures
matched vertex/fragment „fixed” chain… so at
the beginning all the data was processed in Pixel units
„vertex units” and then it was moved to
fragment units.

5.  SISD – Single Instruction Single Data
 Standard way… one instruction is being executed
per single data.
 SIMD – Single Instruction Multiple Data
 Instruction is being executed per several data –
like for one 4D vector (128 bits)
 MIMD – Multiple Instructions Multiple Data
 Parrarel processing!

6. Vertex units used Units
Dynamic task division…
Fragment units used Vertex units used
u n u s e d fragment units used
Effect that uses a lot vertex processing Effect that uses a lot vertex processing
Vertex units used Units
Fixed task division…
u n u s e d
Fragment units used fragment units used
vertex units used
Effect that uses a lot fragment processing Effect that uses a lot fragment processing
Vertex units/Fragment units and their quantities were fixed – we had N vertex processors, and M
fragment processors, but now we have unifed architecture. That means that we have K units
that can process vertex and fragments… there is no difference between them.

7. Controller
Stream processors
As we can see there are no
vertex/fragment units… instead there Shared memory
are stream processors that can handle
both vertex and fragments… and even
more.

8.  Scalars… not Vectors!
 Stream processor uses only one data per
instruction.
 But we have a lot of SP!
 SP gives far more great flexibility.
 GPGPU
 SIMT – Single Instruction Multiple Threads

9.  New architecture - NV
 DX11, OpenCL
 Miltithreaded Rendering
 Rendering commands can be called from difrent threads
 3 000 000 000 transistors!
 End of 2009? End of winter 2010? Never?
 Double precission callculations cost twice as much as float,
not ten times as it was before!
 Debugging – one can debug gpu directly from VisualStudio

10. Fragment
Vertex Shader
Shader
Geometry
Shader
CUDA
Unified Shader OpenCL
DirectX Compute
ATI Stream

11.  General-purpose computing on graphics
processing units
 Kernels – code that will be executed on the
GPU
 Not only graphics but also:
 Physics
▪ Fluids
▪ Collisions
▪ N-body simulations…
 Financial
 Speach/Pattern recognition
 Phenomena modelling – weather…
 Neural nets
 AI

12.  Use as few as possible:
 calculations
 Huge textures – mimpaps instead
 interpolators
 Data
 Rendering state changes
 Dynamic Vertex Buffers
 Textures… use texture atlases maybe
 Texture fetches
 Use more:
 Batches
 Triangle stripes

13.  Use Maths
Uniform sphere:
p = sqrt(Rx^2 + Ry^2 + (Rz + 1)^2) =
sqrt(Rx^2 + Ry^2 + Rz^2 + 2Rz + 1);
R vector is normalized so: Rx^2 + Ry^2 + Rz^2 = 1
p = sqrt(2 * (Rz + 1)) = 1.414*sqrt(Rz + 1)
Calculte this before it
is send to the gpu!
 Reduce calculation on uniform vars!
half4 main(float2 diffuse : TEXCOORD0,
uniform sampler2D diffuseTex,
uniform half4 g_OverbrightColor) {
return tex2D(diffuseTex, diffuse) * g_OverbrightColor * 3.0;
}
 Normalize
dot(normalize(N), normalize(L)) uses two sqrts!
but:
(N/|N|) dot (L/|L|) = (N dot L) / (|N| * |L|) = (N dot L) / (sqrt( (N dot N) *
(L dot L) ) = (N dot L) * rsq( (N dot N) * (L dot L) )
Now we have only one sqrt – three dots are much cheaper than sqrt

14.  Texture lookups:
 ~ 10 : 1 (ALU:Sampler)
 Normalization cube map
 Single „Dot” is not worth texture lookups…
 But calculation of NormalDistribution… YES!
 Early Z-Test
 Depth-only Rendering, then full scene (for the
second time)

15.  Lighten number of attributes – „pack” them as possible.
 float4 myData is better than:
▪ float3 myDataOne;
▪ float1 myDataTwo;
 But do not pack in interpolators
 Use as few scalars as possible
 When vectors are packed no optimalizations can be performed
 What do you really need?
 Normal, binormal, tangent… no! You need only two of them!
 Binormal = normal _Cross_ Tangent

16. PerfKit
•For DirectX mostly
•Little support for OpenGL – via glExpert
PiX for Windows
•Shows everything! But only for Windows, DirectX…
AMD GPU Perf
Similar to Pix, but for
OpenGL… 800$ ;(

17. GLIntercept
• OpenGL
• free 
• log every call of opengl command
• edit shaders in realtime
• although it is a bit simple it has a
powerful impact on debugging…

18. GPU ShaderAnalyzer
• free, from AMD!
• glsl/hlsl
• shows number of asm instructions
• ALU, TEX instructions, etc..
• bottlenecks

19. FXComposer, by
NVidia
ShaderDesigner
by TyphoonLabs
RenderMonkey
by AMD/ATI

20.  PPAM – slajdy -
PARALLEL PROCESSING AND APPLIED MATHEMATICS, Wrocław 2009
 Developer.nvidia.com
 glintercept.nutty.org
 developer.amd.com
 Nvidia GeForce GTX 260/280 Review