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Re: [Xen-devel] xen.git branch reorg

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] xen.git branch reorg
From: Christophe Saout <christophe@xxxxxxxx>
Date: Sat, 25 Apr 2009 00:39:22 +0200
Cc: bderzhavets@xxxxxxxxx, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>
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Hi Jeremy,

> >  In meantime time i see,  that 2.6.30-rc3&rc2&rc1-tip are affected.
> > Solution is the same as on Solaris xVM Linux DomUs about one
> > year ago -  is  to disable checksum (nothing else) offloading at Linux 
> > DomUs ( CentOS 5.3, Ubuntu 9.04)
> >
> > /usr/local/sbin/ethtool -K etho tx off
> OK, that's a good lead.

Yes, I've been seeing this too (and meant to investigate it before
claiming there's abug) and I can confirm that turning off segmentation
offloading "cures" the problem here too.

Now the tcpdump on Dom0 looks interesting.  It repeatedly sees a packet
with 2880 byte from DomU coming in, which is then dropped and ICMP
"fragmentation needed" sent back, the DomU resends a 1440 byte packet
(after some delay), which then goes through, but then the next one is a
2880 byte one again, and so on.

FYI: My Dom0 is running NAT, in case this is relevant.


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