The new API Overhead feature test for 3DMark was developed with input from AMD, Nvidia, Intel, Microsoft and other members of the Futuremark Benchmark Development program and compares the relative performance of DirectX 11, DirectX 12 and Mantle on a single system.
Since the new API Overhead feature test is not a general-purpose GPU benchmark, according to Futuremark, it should not be used to compare graphics card from different vendors as Futuremark is promising a DirectX 12 benchmark with game-like workloads, which should be available after the public launch of Windows 10 OS.
According to Futuremark, API overhead is quite important and with the recent talk that new graphics APIs let developers get "close to the metal", something that we have seen with AMD's Mantle API and will see with DirectX 12. Lower overhead can be achieved by making better use of multi-core CPUs, which eliminates software bottlenecks, especially with draw calls.
Futuremark explained that these draw calls occur when the CPU tells the GPU to draw an object on the screen and with game typically making thousand of draw calls per frame, these also create performance-limiting overhead for the CPU. With the ever rising number of draw calls, graphics engines are limited by API performance and the result of the new test shows the maximum number of draw calls per second by each API before the frame rate drops below 30 FPS.
In order to run the new 3DMark API Overhead feature-set DirectX 12 test you'll need up-to-date Windows 10 Technical Preview (build 10041 or later), 4GB of RAM, and DirectX feature level 11_0 graphics card. For the Mantle test, you'll need 4GB of RAM and, of course, AMD GPU with support for Mantle API, while the DirectX 11 test also needs 4GB of RAM and DirectX feature level 11_0 hardware with at least 1GB of VRAM.
The new 3DMark update v1.5.884 also fixes a bug that could cause the Sky Diver demo to hang at the cave entrance scene as well as adds some other minor updates.
The API Overhead feature test is available now in the latest version of 3DMark Advanced Edition and 3DMark Professional Edition while the Steam version of 3DMark updates automatically. Unfortunately, it is not available for the free 3DMark Basic Edition or the Steam demo.