I am doing a vga passthru test on a HP Z800 workstation which has:
Intel 5520 chipset (rev 13)
Xeon X5680 CPU
nvidia quadro fx5800 gfx card
win2003 x64 guest
, but after passthru the vga card to vm, the vm run very slow, the cpu ut is very high for any operation in guest. some clues from my investigation:
1. guest reponse speed has relationship with the virtual memory assigned to it, e.g, a 4G VM is faster than a 8G VM.
2. another machine with Intel 5500(rev 22) has no this problem.
3. check xen dmesg, the snoop control was not enable, but the 5500(rev 22) machine has snoop control enabled.
From the document at http://www.intel.com/Assets/PDF/specupdate/321329.pdf, there is a defect: "Bandwith very slow for write traffic with noSnoop attribute set", does my problem relate to the defect? if yes, how to resolve it?
It seems the revision 22 fixed it?
rev 13 -> b3 step
rev 22 -> c2 step
So the 5500/5520 b3 step doesn't vt-d snoop control?