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Low-Level Test Results: Driver Overhead

GFXBench 3.0: A Fresh Look At Mobile Benchmarking
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The Driver Overhead test is an OpenGL-based metric that applies minimal stress to the GPU, but taxes its driver by by rendering lots of simple primitives one by one, changing depth and blend state, plus shader uniform values like position, color, rotation, and size for each of them. The frequency of these state changes reflect real-world applications.

In doing this, the benchmark uses lots of draw calls. Its aim is to measure the summed CPU overhead of those calls, which are largely influenced by the driver. The results show how fast the software processes the various API calls.

We already know that software can have a real impact on performance, both in terms of CPU load and battery drain. Don't believe us? Just check out the whole debate between AMD's Mantle API and DirectX 11. Optimizing the way those calls are handled can really open up a processing bottleneck, resulting in additional performance.

This test measures driver overhead by rendering a large number of simple objects one-at-a-time, changing the device state for each of them, spitting out a result in total number of frames rendered.

On-Screen

First, the drivers are tested at each device's native resolution.

Apple's iPhone 5s is the clear winner. Its extensive experience with Imagination Technology's hardware and a stable software ecosystem appear to pay off, yielding an almost-25-percent lead over the nearest competitor, EVGA's Tegra Note 7.

The Galaxy Note 10.1” 2014 Edition shows up higher here than in any other test. Whatever sins TouchWiz has committed on performance in previous tests, ARM's Mali driver at least enjoys an advantage when we puts it efficiency to the test.

Fourth spot goes to Oppo's N1, ahead of the Google Nexus 7 by around 24 percent. Because the N1's Snapdragon 600 runs at up to 200 MHz faster than the S4 Pro, we can see why it'd be able to handle more frames, given the same Adreno 320 graphics core. Less clear is why the Nexus 5's Snapdragon 800 would finish second-to-last, unless Qualcomm's Adreno 330 driver just isn't as optimized.

Off-Screen

Now the drivers are tested in a 1080p fixed off-screen resolution.

Taking the operation off-screen at a standardized resolution yields a similar finishing order, except that Apple's iPhone 5s extends its lead to 100 percent over the Tegra Note 7. That's impressive to say the least, but not particularly surprising considering that Apple has been writing and using software-managed OpenGL frame buffers since moving to OS X. 

The Nexus 5 is able to marginally beat the Nexus 7, but still loses out to the Snapdragon 600-equipped Oppo N1.

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