Phoronix published a review on the Are AMD Athlon/Sempron APUs Fast Enough For Steam On Linux, Steam Machines A quote from the article:

Earlier today the latest installment of our extensive Linux testing of AMD's new Athlon AM1 APUs were shared in the form of RadeonSI vs. Gallium3D benchmarks of the Radeon R3 Graphics found with these new entry-level APUs. Not included with that open-source vs. closed-source driver testing was any Source Engine / Steam Linux game testing due to an XCB DRI3 issue, but this article is devoted to looking at the Catalyst performance for the Sempron 2650, Sempron 3850, Athlon 5150, and Athlon 5350 to see whether any of these APUs can make the cut for a budget Steam Machine.

With all four of these brand new AMD AM1 APUs bearing Radeon R3 Graphics, they were tested using the Catalyst Linux driver (fglrx 13.35.5 / OpenGL 4.3.12798) when using Ubuntu 14.04 LTS. The games tested were Counter-Strike: Source, Half-Life 2: Lost Coast, and Portal. With each of these Valve Source Engine games we benchmarked them at six different resolutions: 1024 x 768, 1280 x 960, 1600 x 900, 1280 x 1024, 1680 x 1050, and 1920 x 1080. This way we can see quite well if there's CPU/GPU bottlenecks and at what resolutions (if any) the APUs deliver playable frame-rates with the Catalyst Linux driver. As outlined in the article earlier today, the Catalyst driver is still significantly faster than RadeonSI Gallium3D for these new AMD APUs.

 Are AMD Athlon/Sempron APUs Fast Enough For Steam On Linux, Steam Machines @ Phoronix