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xen-users
Re: [Xen-users] Xen4.0.1 : slow Disk IO on DomU
I've found that my motherboard with AMD890GX chipset doesn't support
IOMMU virtualisation ( (XEN) I/O virtualisation disabled )
Can you tell me if yours is supporting it ( xm dmesg |grep 'I/O
virtualisation' )
Thanks
Le 18/03/2011 19:14, Erwan RENIER a écrit :
Le 18/03/2011 09:00, Joost Roeleveld a écrit :
On Thursday 17 March 2011 18:31:10 Erwan RENIER wrote:
Le 17/03/2011 09:31, Joost Roeleveld a écrit :
On Wednesday 16 March 2011 23:31:31 Erwan RENIER wrote:
Hi,
When i test the IO bandwidth it's pretty much slower on DomU :
Dom0 read : 180MB/s write : 60MB/s
DomU read : 40MB/s write : 6MB/s
Just did the same tests on my installation (not yet on Xen4):
Dom0:
# hdparm -Tt /dev/md5
/dev/md5:
Timing cached reads: 6790 MB in 1.99 seconds = 3403.52 MB/sec
Timing buffered disk reads: 1294 MB in 3.00 seconds = 430.94
MB/sec
(md5 = 6-disk RAID-5 software raid)
# hdparm -Tt /dev/vg/domU_sdb1
/dev/vgvg/domU_sdb1:
Timing cached reads: 6170 MB in 2.00 seconds = 3091.21 MB/sec
Timing buffered disk reads: 1222 MB in 3.00 seconds = 407.24
MB/sec
DomU:
# hdparm -Tt /dev/sdb1
/dev/sdb1:
Timing cached reads: 7504 MB in 1.99 seconds = 3761.93 MB/sec
Timing buffered disk reads: 792 MB in 3.00 seconds = 263.98
MB/sec
Like you, I do see some drop in performance, but not as severe as you
are
experiencing.
DomU disks are Dom0 logical volumes, i use paravirtualized guests,
the
fs type is ext4.
How do you pass the disks to the domU?
I pass them as such:
disk = ['phy:vg/domU_sda1,sda1,w',
(rest of the partitions removed for clarity)
My DomU conf is like this :
kernel = "vmlinuz-2.6.32-5-xen-amd64"
ramdisk = "initrd.img-2.6.32-5-xen-amd64"
root = "/dev/mapper/pvops-root"
memory = "512"
disk = [ 'phy:vg0/p2p,xvda,w' , 'phy:vg0/mmd,xvdb1,w',
'phy:sde3,xvdb1,w' ]
vif = [ 'bridge=eth0' ]
vfb = [ 'type=vnc,vnclisten=0.0.0.0' ]
keymap = 'fr'
serial = 'pty'
vcpus = 2
on_reboot = 'restart'
on_crash = 'restart'
seems ok to me.
Did you pin the dom0 to a dedicated cpu-core?
Nop
Either you are hitting a bug or it's a configuration issue.
What is the configuration for your domU? And specifically the way you
pass the LVs to the domU.
As you can see :
xvda is a lv exported as a whole disk with lvm on it, so xvda2 is
a lv
from a vg in a lv ( ext4 => lv => vg => pv => virtual disk =>
lv =>vg
=>pv => raid5 =>disk )
xvdb1 is a lv exported as a partition ( ext4 => virtual part => lv
=> vg
=> pv => raid5 => disk )
xvdb2 is a physical partition exported as a partition ( ext3 =>
virtual
part => disk )
Curiously it seems the more complicated, the better it is :/
Yes, it does seem that way. Am wondering if adding more layers
increases the
amount of in-memory-caching which then leads to a higher "perceived"
performance.
One other thing, I don't use "xvd*" for the device-names, but am
still using
"sd*". Wonder if that changes the way things behave internally?
I doesn't change with sd*
I noticed that the cpu io wait occurs in domU ,nothing happen in dom0
Does someone knows a way to debug this ? at kernel level or in the
hypervisor ?
By the way how to get the hypervisor activity i don't think it
appears in dom0.
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