Tessellation Performance
Given the emphasis that AMD originally put on tessellation in DirectX 11 and the emphasis Nvidia now puts on tessellation in DirectX 11, I like to run each new card through a worst-case to gauge the effect of each company’s architecture on geometry performance. That used to be Unigine's Heaven demo. But now that an actual playable title is available in HAWX 2, I've shifted away from the pure synthetic.
In Nvidia’s case, it’s interesting to see how frame rates scale up and down based on the number of PolyMorph engines enabled in each design. We’ve found in the past that the Fermi architecture doesn’t necessarily scale as linearly as Nvidia might suggest. That’s manifest in the fact that GeForce GTX 570’s GF110 processor offers 15 PolyMorph engines. The GeForce GTX 560 features eight. And there’s only a single percentage point of scaling difference in HAWX 2, shifting from tessellation off to on. Clearly, geometry isn’t the bottleneck.
AMD’s situation isn’t much clearer. Cayman was supposed to introduce a second tessellation unit, whereby Barts only offers one. And yet, Barts scales better. The only real constant is that the Cypress architecture suffers most when tessellation is applied. Radeon HD 5870 cards are a great deal right now—especially when you can find them with fat rebates tacked on. But should more developers follow Ubisoft’s lead in HAWX 2 with massive geometry, it’ll take a bigger performance hit than the more optimized Radeon HD 6000-series boards.
