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5520 chipset (rev 13) vt-d snoop issue

Community Manager


I am doing a vga passthru test on a HP Z800 workstation which has:

Intel 5520 chipset (rev 13)

Xeon X5680 CPU

32G memory

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, 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?

Thank you,

Jin Cui

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2 Replies


The situation you describe may very well match that stated on Errata # 24 on the Specification Update document you referred to, and thus, as a recommendation, I'd suggest making sure the BIOS is updated, and if you've already done this, then, please, contact either your place of purchase or HP for board-wise troubleshooting and/or advice.

Community Manager

Yesterday, I updated BIOS to the last version, but the problem still there.

I also had try the workaround of Errordata # 24 (set the PERFCTRLSTS register bit 3 and 2 set to 0), it doesn't help. Actually, they are already set to 0 by default.

Any information about changes from rev 13(B3) to rev 22(C2)? add snoop control feature? Thanks you very much!