[Xen-devel] Re: vga passthrough on some graphic card result in guest slow

["Jin Cui" <generalking@xxxxxxx>]

Hello,

 

I think I got the reason. There is no snoop control support on my VT-d hardware. From xm dmesg I got "Intel VT-d Snoop Control not enabled" message.

Check xen code, if no snoop control hardware, xen will trigger wbinvd operation at all cpu, this downgrad the performance.

As some IOH chipset, like Intel 5520, they don't need snoop, should xen handle this?

 

Thanks,

Jin

----- Original Message -----

From: Jin Cui

To: xen-users@xxxxxxxxxxxxxxxxxxx ; xen-devel@xxxxxxxxxxxxxxxxxxx

Sent: Wednesday, May 04, 2011 4:43 PM

Subject: vga passthrough on some graphic card result in guest slow

Hello,

 

I have tried vga passthrough on my open suse11.4(xen4.0.2) today. (vga card: nvidia QuadroFX5800) After enable vga passthrough, the guest VM(windows2003x64) becomes very slow for any operation including OS startup, mouse moving. And the guest's CPU utilization always keeps high(40% +), it should be consumed by windows kernel because I didn't see any process use such cpu resource from task manager. But this issue is not happen on another QuadroFX1800 machine, does vga passthrough depends on graphic hardware? since 5800 has 4G video memory but 1800 only has 768M. My guest configuration as below:

 

name="w2k3x64_2"
description="None"
uuid="dd12d5fa-57d0-9a56-8cbb-44495f9fecd3"
memory=4096
maxmem=4096
vcpus=4



localtime=1
keymap="en-us"

builder="hvm"
device_model="/usr/lib/xen/bin/qemu-dm"
kernel="/usr/lib/xen/boot/hvmloader"
boot="c"
disk=[ 'phy:/dev/lvm/win2003,hda,w',]
vif=[ 'mac=00:16:3e:7b:07:29,bridge=br0,model=rtl8139', ]
gfx_passthru=1
pci=['03:00.0']

stdvga=0
vnc=1
vncunused=1
viridian=0
usb=1
acpi=1
pae=1

usbdevice='tablet'

serial="pty"

 

Thank you,

Jin

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