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.

Currently Xen only allows a single device emulator to be attached to each HVM guest in a system and, to date,
this has been QEMU generally running as a process in the same domain as the toolstack, or in a stub domain.

To enable the deployment of virtual GPUs to HVM guests in XenServer, patches were created to allow multiple device emulators to be attached to each HVM guest. QEMU continues to be used to emulate the majority of the devices, but a second process is spawned to handle the virtual GPU. This opens up the possibility of the GPU vendors supplying 'appliance' driver domains in future.

I'd like to give an overview of the changes that we've made to Xen and QEMU to enable the use of multiple emulators, the potential benefits to driver domains, plus the knock on effect of emulator disaggregation on the 'unplug' protocol and what we could do about this.

GPU virtualization has become an increasingly important requirement for client virtualization and cloud. Significant challenges exists realizing the multiplexing of graphics, media and compute workloads from multiple VMs and achieving the goals of being fully functional, high performance and secure. In this presentation, we will first review existing graphics virtualization technologies, and then introduce how XenGT - an open source solution from Intel - approaches differently. Broad functionality and good performance is achieved by accelerating the native OS graphics stack in each VM with minimum hypervisor intervention. A software mediator ensures the secure multiplexing of workloads from the multiple VMs by managing the scheduling of VMs on the GPU and controlling access to privileged resources and operations.