[CentOS-virt] Windows Xen VM's have high guest CPU usage and poor performance

Ryan Pugatch rpug at linux.com
Thu Jan 21 03:18:06 UTC 2010

Hello all,

I have a PowerEdge 2950 that I am using to host Windows XP VM's under 
CentOS.  I am experiencing poor performance in the Xen VM's.  Any time I 
try to do something, the CPU usage (as reported by the Windows task 
manager) hits 100% for a few and then drops back down.  This is causing 
the VM's to run sluggish and be quite annoying to use.  Example.. I 
click IE.. cpu hits 100% and IE takes a bit to open.  I go to a 
website.. 100%.. I click a link.. 100%. This is the case even if I only 
have one VM running.

I now have 32 VM's running on the machine and dom0's cpu usage as 
reported by xm top is 622%.  It seems like Xen is just performing poorly 
while handling these Windows VMs.  Any suggestions?  I have Windows VM's 
on other hardware (typically PowerEdge R905s and R710s and they seem ok).

This 2950 is a decent machine.. 32G RAM, 2x Xeon E5405 (quad core) at 
2ghz.  And I'm only allocating 1 CPU and 768MB RAM for each VM.

Sample config:

name = "win01n"
maxmem = 768
memory = 768
vcpus = 1
builder = "hvm"
kernel = "/usr/lib/xen/boot/hvmloader"
boot = "c"
pae = 1
acpi = 1
apic = 0
localtime = 1
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
device_model = "/usr/lib64/xen/bin/qemu-dm"
usbdevice = "tablet"
sdl = 0
vnc = 1
vncunused = 0
vncdisplay = "1"
disk = [ 'file:/var/xen/running/win01n,ioemu:hda,w' ]
vif = [ "bridge=xenbr0" ]
serial = "pty"

Thanks in advance for any insight!

	- Ryan

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