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

To: <bderzhavets@xxxxxxxxx>, "'Jeremy Fitzhardinge'" <jeremy@xxxxxxxx>, "'Christophe Saout'" <christophe@xxxxxxxx>
Subject: RE: [Xen-devel] xen.git branch reorg
From: "Venefax" <venefax@xxxxxxxxx>
Date: Sat, 25 Apr 2009 03:03:28 -0400
Cc: 'Xen-devel' <xen-devel@xxxxxxxxxxxxxxxxxxx>, 'Ian Campbell' <Ian.Campbell@xxxxxxxxxx>
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What are the exact commands to turn off Segmentation Offload and Checksum Offload?

Also, should this be done only at Dom0 or also at DomU’s?

Is this correct or should it be “eth0”?


/usr/local/sbin/ethtool -K etho tx off


From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Boris Derzhavets
Sent: Saturday, April 25, 2009 2:55 AM
To: Jeremy Fitzhardinge; Christophe Saout
Cc: Xen-devel; Ian Campbell
Subject: Re: [Xen-devel] xen.git branch reorg



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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