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Texture filtering

Peak bilinear
filtering
(Gtexels/s)
Peak bilinear
FP16 filtering
(Gtexels/s)
Memory
bandwidth
(GB/s)
GeForce GTX 280 48 24 142
GeForce GTX 480 42 21 177
GeForce GTX 580 49 49 192
Radeon HD 5870 80 40 154
Radeon HD 6970 85 42 176
Radeon HD 7970 118 59 264

Now that we've talked about the architecture ad nauseum, it's nice to get into some test results. On paper, Tahiti has massive texture filtering throughput compared to any other current GPU, and in this quick synthetic test, it delivers on that promise quite nicely. The only saving grace for the competition is the GF110's full-rate FP16 filtering, which allows the GeForce GTX 580 to avoid being completely embarrassed.

Tessellation and geometry throughput

Peak
rasterization
rate
(Mtris/s)
Memory
bandwidth
(GB/s)
GeForce GTX 280 602 142
GeForce GTX 480 2800 177
GeForce GTX 580 3088 192
Radeon HD 5870 850 154
Radeon HD 6970 1760 176
Radeon HD 7970 1850 264

Given that Tahiti has substantially more buffering for geometry expansion than its predecessors, we'd expected the 7970 to perform better in this test. Instead, it's not much faster at the "Extreme" tessellation level—and is actually slower at the lower "Normal" setting. Our sense is that this result may be caused by a software quirk, at least in part. TessMark is written in OpenGL, and AMD's driver support there doesn't always get the attention the DirectX drivers do.

We do have another option, which is to try a program that can act as a tessellation benchmark via DirectX 11. Unigine Heaven fits the bill by offering gratuitous amounts of tessellation on its "Extreme" setting. The additional polygons don't really improve image quality in the demo, which is a shame, but they do push the graphics hardware pretty hard, so this demo will serve our need for a synthetic test of geometry throughput.

Now that's more like it. The 7970 shows major improvement over the past two generations of Radeon graphics hardware, enough to put it at the front of the pack. Now, I'm not convinced Tahiti is outright faster than the GF110 in tessellation throughput. The Heaven demo includes things other than ridiculous numbers of polygons, including lots of pixel shader effects. My sense is that the tessellation hardware on the top few GPUs is simply fast enough that something else, like pixel shader performance, becomes the primary performance limiter. When that happens, Tahiti's massive shader array kicks in, and the contest is over. The relevant point is that Tahiti's geometry throughput is sufficiently improved that it's not an issue, even with an extremely complex tessellation workload like this one.