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

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Christophe Saout <christophe@xxxxxxxx>
Subject: Re: [Xen-devel] xen.git branch reorg
From: Boris Derzhavets <bderzhavets@xxxxxxxxx>
Date: Fri, 24 Apr 2009 23:55:19 -0700 (PDT)
Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>
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I have to apologize. Turning off segmentation offloading may work as well.
Just now it fixed VNC issue on bare metal - CentOS 5.2 with Atansic Gigabit
Ethernet driver (ASUS P5KR) . I gonna try it at DomUs at my earliest convenience.


--- On Fri, 4/24/09, Christophe Saout <christophe@xxxxxxxx> wrote:
From: Christophe Saout <christophe@xxxxxxxx>
Subject: Re: [Xen-devel] xen.git branch reorg
To: "Jeremy Fitzhardinge" <jeremy@xxxxxxxx>
Cc: bderzhavets@xxxxxxxxx, "Xen-devel" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "Ian Campbell" <Ian.Campbell@xxxxxxxxxx>
Date: Friday, April 24, 2009, 6:39 PM

Hi Jeremy,

> > In meantime time i see, that 2.6.30-rc3&rc2&rc1-tip are
> > Solution is the same as on Solaris xVM Linux DomUs about one
> > year ago - is to disable checksum (nothing else) offloading at
> > 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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