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xen-users
Re: [Xen-users] Re: Performance Issues: I/O Wait
Xen can exacerbate Linux SMP issues. Do you have hyperthreading turned
on in your CPU's? If so, at least for testing, try turning it off.
Also, beyond turning of the TX offloading in both the dom0 and domU,
is there any chance that there's another device attached to that
bridge which would cause network delays? In particular, is there a
device that may incorrectly see the domU IP as coming from the dom0
due to an ARP conflict? I see that you've specified a fixed MAC
address. Is there any chance that that same MAC address is used by the
dom0? Perhaps the initrd is the one from dom0 and its got the MAC
address set in the initrd to be the same as the one in the dom0?
Try tcpdumping from both domains and see if you see any
retransmissions, or perhaps even a smoking gun like a system ARPing
for itself when it should know better.
It's also possible that there's a transmission size problem. There
have been reported problems of dom0<->domU traffic not honoring the
MTU of the bridge or virtual device, which then forces retransmission
when the receiving side cannot handle the larger buffer.
If NFS, try changing from TCP to UDP or modifying the rsize and wsize
buffering to fit within the MTU of your (virtual) ethernet devices.
Hope this helps,
-Steve Senator
Quoting Nick Couchman <Nick.Couchman@xxxxxxxxx>:
Hi, again...haven't had any responses to this, yet.
Nick Couchman 10/18/07 11:05 AM >>>
Hey, everyone,
I'm having some issues with a Xen DomU right related to performance.
... The culprit seems to be high I/O wait times related to the
network interface.
The host machine is a Dell PowerEdge 1950 with 2 x Dual-Core Xeon
processors (Xeon 5150 @ 2.66GHz, 1333 FSB). ... Building these
Linux distributions on the physical system takes 70-80 minutes
(real time) - on the DomU system it takes 130-140 minutes.
...
vif=[ 'mac=00:16:3e:75:0d:be,bridge=xenbr108', ]
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