Nouveau, the reverse-engineered NVIDIA Linux graphics driver, also has measurable performance overhead with tossing XMir into the rendering equation. With having an extra step to get the contents out to the screen, OpenGL games are noticeably slower than if running on an X.Org Server communicating directly with the graphics hardware. The benchmarks were done just like the Intel Sandy Bridge testing but when running the Nouveau graphics driver atop a mobile NVIDIA Quadro graphics processor found in a Lenovo ThinkPad W510 laptop.
The Ubuntu 13.10 and Mir/XMir packages were as of 28 June with the Linux 3.10 kernel and Mesa 9.2-devel Nouveau Gallium3D. Testing was done with X.Org Server 1.13.3 and then when the Unity 7 desktop was running through XMir. All benchmarking was handled via the Phoronix Test Suite software.
Unfortunately, the Nouveau Mir support isn't as good as with the Intel driver. For some games like Doom 3 and Xonotic when attempting to launch them with the Nouveau graphics driver on XMir, the session would crash. These games would run fine on the same hardware and driver with Mir out of the equation. In addition, due to a number of Phoronix readers and Twitter followers reporting XMir problems with open-source Radeon graphics, benchmarks with AMD graphics hardware on XMir will not come until a later date. Likewise, benchmarks of Mir with the proprietary NVIDIA and AMD Catalyst drivers won't come until there is driver support.