Ever since virtualization hype begun I have wondered how to improve GPU performance of guest systems.
The workstation that I've set up has some specifics that allow me to forward the second GPU to any of the guest systems running with KVM. The specifics are having an IOMMU function available and enabled in BIOS and having two GPU cards, one of which has to be one the later AMD Radeon series. So you need a pretty good mainboard plus two GPUs.
Here's what I've set up:
ASUS Sabretooth 990FX
Nvidia Quadro FX 380 (linux)
Club3D Radeon HD 7750 1GB (windows guest)
You can use any mainboard that supports IOMMU and multiple GPUs.
I only have one problem that keeps me from fully enjoying this setup. Each time I shut down the windows guest the host machine freezes on reboot or when I try to run windows guest for the second time. So I can only run windows guest with the dedicated GPU once each time I boot up. There's no problems when I do not run the guest or when the guest runs all the time.