This week during SIGGRAPH, Intel demonstrated the upcoming DirectX 12 API using a Surface Pro 3 that was thermally controlled to mimic 10 to 15 minutes of gameplay. The demo provided two modes – performance and power- to show how the new API handles each. The demo could also instantly switch from DirectX 12 to DirectX 11 to see the performance and power gains with the former.
The DirectX demo consisted of a space scene filled with 50,000 “dynamic and unique” asteroids. In performance mode, DirectX 11 rendered the scene at 19 frames per second, and the power usage was equally distributed between the CPU and GPU. However, when switched over to DirectX 12, the framerate jumped from 19 fps to 33 fps, a 70 percent increase.
According to Intel’s Andrew Lauritzen, the performance increased because DirectX is designed for “low overhead, multi-threaded” rendering. Because the CPU power has been reduced, that leftover power can be used by the GPU.
For the second power-focused demo, Intel used the same scene, only the framerate was locked. At the bottom right of the screen, you can see that DirectX 11 requires nearly equal amounts of power; however, with DirectX 12 turned on, the overall power draw is reduced, with the CPU sipping on power and the GPU getting a bigger fill. Thus, when you compare the two APIs together, the tablet will stay cooler and have a longer battery life when the application uses DirectX 12.
“The main takeaway is that power and performance are inseparably linked. Conventional notions of 'CPU vs. GPU bound' are misleading on modern devices like the Surface Pro 3," Lauritzen said. "An increase in CPU power efficiency can be used for more performance even if an application is not 'CPU bound'".
Intel plans to release the demo when Microsoft finally launches DirectX 12. Additional images can be found on Lauritzen’s blog.