XenServer PCI Passthrough

You should have heard about SR-IOV or PCI passthrough. Everything has been said about these technologies so nothing new here. This is just a simple bookmark, or, if you will, yet another copy-paste.

Xen PCI Passthrough

PCI passthrough allows you to give control of physical devices to guests: that is, you can use PCI passthrough to assign a PCI device (NIC, disk controller, HBA, USB controller, firewire controller, soundcard, etc) to a virtual machine guest, giving it full and direct access to the PCI device.
This has several potential uses, including the following:

• One of the major overheads of virtual networking is the unavoidable overhead of copying; passing through a network card directly completely avoids this overhead.
• Passing through graphics cards to guests allows them full access to the 3D acceleration capabilities. This can be useful not only for desktops, but also to enable Virtual Desktops for high-end CAD users, for example.
• You can set up a Driver Domain, which can increase both security and reliability of your system. 

Pic taken from Red Hat

The whole article is at Xen wiki