Exploring DirectX 12: 3DMark API Overhead Feature Test

Closing Thoughts

Wrapping things up, Futuremark’s latest benchmark certainly gives us a new view on DirectX 12, and of course another data point in looking at the performance of the forthcoming API.

Since being announced last year – and really, since Mantle was announced in 2013 – the initial focus on low-level APIs has been on draw call throughput, and for good reason. The current high-level API paradigm has significant CPU overhead and at the same time fails to scale well with multiple CPU cores, leading to a sort of worst-case scenario for trying to push draw calls. At the same time console developers have low enjoyed lower-level access and the accompanying improvement in draw calls, a benefit that is an issue for the PC in the age of so many multiplatform titles.

DirectX 12 then will be a radical overhaul to how GPU programming works, but at its most basic level it’s a fix for the draw call problem. And as we’ve seen in Star Swarm and now the 3DMark API Overhead Feature Test, the results are nothing short of dramatic. With the low-level API offering a 10x-20x increase in draw call throughput, any sort of draw call problems the PC was facing with high-level APIs is thoroughly put to rest by the new API. With the ability to push upwards of 20 million draw calls per second, PC developers should finally be able to break away from doing tricks to minimize draw calls in the name of performance and focus on other aspects of game design.

GDC 2014 - DirectX 12 Unveiled: 3DMark 2011 CPU Time: Direct3D 11 vs. Direct3D 12

Of course at the same time we need to be clear that 3DMark’s API Overhead Feature Test is a synthetic test – and is so by design – so the performance we’re looking at today is just one small slice of the overall performance picture. Real world game performance gains will undoubtedly be much smaller, especially if games aren’t using a large number of draw calls in the first place. But the important part is that it sets the stage for future games to use a much larger number of draw calls and/or spend less time trying to minimize the number of calls. And of course we can’t ignore the multi-threading benefits from DirectX 12, as while multi-threaded games are relatively old now, the inability to scale up throughput with additional cores has always been an issue that DirectX 12 will help to solve.

Ultimately we’re looking at just one test, and a synthetic test at that, but as gamers if we want better understand why game developers such as Johan Andersson have been pushing so hard for low-level APIs, the results of this benchmark are exactly why. From discrete to integrated, top to bottom, every performance level of PC stands to gain from DirectX 12, and for virtually all of them the draw call gains are going to be immense. DirectX 12 won’t change the world, but it will change the face of game programming for the better, and it will be very interesting to see just what developers can do with the API starting later this year.