Xen Project Developer Summit

The current state-of-the-art in displaying guest video is to copy pixel data from domU memory into a buffer in the device model domain, and then to render the display using something like X, or VNC. The quantity of data copied is partially mitigated by dirty page tracking. However when using the VM to play video or other other tasks that require frequent full-screen updates, copying is a significant drag on system performance and power consumption. By using the DRM subsystem in dom0 on systems with a unified memory architecture, it is possible to make arbitrary pages available for direct scanout by the graphics hardware. The in-kernel graphics drivers make this relatively straight forward and maintainable. This presentation explains how the current display path works, and how to use DRM to improve it.