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Aqua Costa

[DirectX 10] ALU- or texture-fetch bound shaders

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[font="Arial"]What does ALU or texture-fetch bound shaders mean?


[size="2"]How do I identify if a shader is either ALU or texture-fetch bound? And how do I improve shader performance based on that?[/size]

[size="2"]Thanks[/size][/font]

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[quote name='TiagoCosta' timestamp='1307472869' post='4820628']
[font="Arial"]What does ALU or texture-fetch bound shaders mean?
[/quote]

Fancy terminology aside, it basically means that your graphics card is the limiting factor to your game's performance (so you're GPU bound), either being very busy with the computations in the shader (that'd be ALU bound) or busy pulling in (or waiting on) texture information. To paint a complete picture, I think the latter case could be either a bandwidth problem (pulling in too much texture data) or a latency problem (either sampling many different textures or random non-sequential access to the texture, both typically killing the cache).

[quote]
[size="2"]How do I identify if a shader is either ALU or texture-fetch bound? And how do I improve shader performance based on that?[/size]
[/font][/quote]

I don't know of any elegant way of determining this, so I'd try setting only 1x1 textures on the shader. These should solve both potential texture-fetch problems, so if the performance is still bad you'd be ALU bound. This would mean you need to optimize (or simplify) the shader code so it runs more smoothly (or up your minimum requirements =). If the performance improves, you probably have a texture-fetch problem on your hands. I don't have any good generic tips on this, but you'd obviously want to make sure that you're using mipmaps and that your texture sizes aren't too extreme. If you happen to be sampling many different textures (and are probably blending them together), it might be worthwhile to check if you can combine them as a pre-processing step.

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