Texture Filtering Performance

Here we'll take a look the the rendering performance of the 6800 Ultra under a few different texturing scenarios.

3DMark03 - GT2 1600x1200, Trilinear Filtering Optimised Normal % Drop
1X 54.3 53.5 -1.5%
16X 40.1 38.9 -3.0%

Throughout the game tests used here we enabled full Trilinear filtering, as opposed to the optimised mode that is enabled by default. This test shows that, in fact, the performance difference with it enabled, at least in the case of 3DMark03's GT2 test, is fairly minimal with only about 1 FPS dropped with either normal rendering or 16X Anisotropic filtering.

SS:SE (FPS) 640x480 800x600 1024x768 1280x1024 1600x1200
Normal 150.3 146.4 141.8 132.7 127.6
8X AF 150.4 148.4 142.6 131.8 116.7
16X AF 150.3 148.0 142.0 131.1 115.0
6800 Ultra % Difference 640x480 800x600 1024x768 1280x1024 1600x1200
8X AF 0.1% 1.4% 0.6% -0.7% -8.5%
16X AF 0.0% 1.1% 0.1% -1.2% -9.9%

We measured the game test with 8X AF enabled for comparison to the FX boards, however here we can see that in our SS:SE game the performance drop for enabling 16X AF over 8X AF is very small, with only the highest resolution showing much performance penalty, and even then is only by 1% or so.

With one of the ALU units in the Pixel Shader having some texture addressing duties as well, the more time spent texturing the more computing power is taken away from the pixel shader. To put this to the test we've taken one of the RightMark 3D shaders and run various levels of Anisotropic filtering on it to see how the performance is altered.

RightMark - Lighting (Phong) - PS2.0 1X 2X 4X 8X 16X
6800 Ultra 167.7 166.8 159.3 153.1 152.7
% Drop from 1X -0.5% -5.0% -8.7% -9.0%
% Drop from Previous -0.5% -4.5% -3.9% -0.3%

As we can see, despite this this test having few texture accesses, but lots of shader math instructions the performance does drop by a maximum of 9% with 16X AF enabled. Bear in mind that the effects of Anisotropic filtering on shader performance will greatly depend on the types of operations in the shader - those with a relatively even ration of texture accesses to ALU operations will have a higher performance hit than shaders that mainly utilise maths operations.

Here we'll test the filtering performance in the more varied environment of 3DMark03's GT2 test.

3DMark03 - GT2, 1600x1200 (FPS) 1X 2X 4X 8X 16X
6800 Ultra 53.2 49.3 43.8 38.5 35.4
% Drop from 1X -7.3% -17.7% -27.6% -33.5%
% Drop From Previous -7.3% -11.2% -12.1% -8.1%

With the more varied conditions of 3DMark03's GT2 test we can see that utilising Anisotropic filtering has a much larger performance hit than in some of the previous cases we've seen, because its a much more varied environment, and probaly more reflective of a number of upcoming games than many of the older fixed function game titles, or those built in the DirectX7 era.