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[Xen-users] Poor disk I/O with HVM stub domains

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Poor disk I/O with HVM stub domains
From: Brian Conway <xen@xxxxxxx>
Date: Thu, 9 Apr 2009 23:30:05 -0400
Delivery-date: Thu, 09 Apr 2009 20:30:57 -0700
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Greetings.  I'm running Xen 3.3.1 on Debian Lenny with the packaged
2.6.26 dom0 kernel on amd64.  Based on some reading [1], I've been lead
to believe HVM device model domains can be a performance win, so I did
some testing on my setup (Intel E8400, 8 GB, single Seagate ES.2 drive,
idle dom0 and WinXP domU).  After following the stubdom README, I saw a
big performance drop-off immediately, so maybe my configuration needs
work.  A quick sequential read/write test with ATTO is below, as well as
configuration files.  The XP instances in question are all clean installs
with indexing turned off and otherwise idle (no significant CPU or disk
utilization).  Prior to jumping into stub domains, this setup has been
100% stable.

Native: http://www.zxvf.us/images/atto-native.jpg

HVM + tap:aio: http://www.zxvf.us/images/atto-hvm-tapaio.jpg

HVM + file:/: http://www.zxvf.us/images/atto-hvm-file.jpg

HVM + tap:aio + stubdom: http://www.zxvf.us/images/atto-hvm-tapaio-stubdom.jpg

HVM + file:/ + stubdom: repeatable blue screen on boot (Partmgr.sys)

# cat winxptest 
kernel = "/usr/lib/xen/boot/hvmloader"
builder = "hvm"
name = "winxptest"
memory = "512"
disk = [ 'tap:aio:/home/xen/winxptest.img,ioemu:hda,w', ]
vif = [ 'type=ioemu,bridge=eth0', ]
vfb = ['type=vnc,vncunused=1']
localtime = 1
boot = "c"
on_reboot = 'restart'
on_crash = 'destroy'
# cat winxpstub
kernel = "/usr/lib/xen/boot/hvmloader"
builder = "hvm"
device_model = "/usr/lib/xen/bin/stubdom-dm"
name = "winxpstub"
memory = "512"
vif = [ 'type=ioemu,bridge=eth0', ]
localtime = 1
boot = "c"
on_reboot = 'restart'
on_crash = 'destroy'
# cat winxpstub-dm 
kernel = "/usr/lib/xen/boot/ioemu-stubdom.gz"
disk = [ 'tap:aio:/home/xen/winxptest.img,hda,w', ]
vif = [ '', 'bridge=eth0', ]
vfb = ['type=vnc,vncunused=1']

Thanks for any tips.

Brian Conway

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