The Reaction Quake 3 game saw its frame-rate drop by over 10% when now being routed through Mir and the unity-system-compositor.
Lastly, Urban Terror and Warsow both saw noticeable performance drops when XMir/Mir was being dealt with.
While XMir is still using an X.Org Server, these results show that for modern Intel Linux graphics there is indeed a performance overhead in dealing with Mir. It will be interesting though to see how the performance is for native Mir applications that don't need to deal with X in the mix, but that's still some months away until more applications will be supported.
These results do show that for at least the time being if migrating an X11 desktop environment to running on XMir, there is a performance penalty without having any real end-user gain. There is a performance cost regardless if the OpenGL game/application is lightweight or more visually demanding upon the graphics stack. Of course, Mir is still early in development, but that's where things stand today and we will definitely be benchmarking Mir as things progress within Ubuntu 13.10 and future releases.
The Canonical Mir team was given a preview of these results hours before this article was published. Kevin Gunn of the Mir team said, "at glance nothing looks completely out of place....except maybe the one nexuiz run, seems odd to be almost double. I suppose we might need to dig into those with >10% delta & determine the limiting factor."
Under the current circumstances, this is a performance regression. It's sad too considering that where Mir is supported right now on the desktop (the open-source Mesa/Gallium3D drivers) the performance is already challenged when compared to the proprietary drivers and now is only being made worse by the Mir overhead. For these open-source Linux graphics drivers, every frame does matter right now for Linux gamers. Meanwhile, the NVIDIA and AMD Catalyst drivers that are already performing great will gracefully fallback to using a pure X.Org Server configuration until they support EGL+Mir. It will also be interesting to see how Wayland and XWayland perform, since Keith Packard among others have made comments in the past that it should be faster than using an outright X.Org Server.
Coming up in July will be Radeon and Nouveau benchmarks of the latest Mir development code atop the latest Ubuntu 13.10 packages at the time. Also to be published in the next day or two are 2D performance benchmarks of Mir/X.Org. Additional test requests can be routed to the Phoronix Forums or @MichaelLarabel on Twitter.