The performance of X typically becomes "abysmal" when it runs on top of another window system like Windows or Mac OS X because the server has to do a lot of bulk memory copies. But, because Wayland is cooperating with X, you get "full speed 2D rendering" while direct rendering is unchanged. Buffer swaps will happen every 16ms, when the X server tells xwayland it has new content and Weston tells the kernel to display it. Putting X atop Wayland will actually "reduce the context switches to once every 16ms", which may make it perform better than native X, Packard said. He doesn't have any numbers, and the effect will likely be imperceptible, but it could be faster. From the audience, Greg Kroah-Hartman also noted that it may result in power savings.