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

To: Venefax <venefax@xxxxxxxxx>
Subject: RE: [Xen-devel] xen.git branch reorg
From: Boris Derzhavets <bderzhavets@xxxxxxxxx>
Date: Sat, 25 Apr 2009 01:35:25 -0700 (PDT)
Cc: 'Xen-devel' <xen-devel@xxxxxxxxxxxxxxxxxxx>
Delivery-date: Sat, 25 Apr 2009 01:35:54 -0700
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I tried at DomU:

1. Specifies whether TX checksumming should be disabled.
# /usr/local/sbin/ethtool -K eth0 tx off

2. Specifies whether TCP segmentation offload should be disabled.
# /usr/local/sbin/ethtool -K eth0 tso off

3.  Specifies whether UDP fragmentation offload should be disabled
# /usr/local/sbin/ethtool -K eth0 ufo off

Second parameter is your Ethernet interface . Might be eth1 or eth2.
Just install ethtool-6 to get  " man ethtool " handy
You can try all of them, just first , second and third.
Whatever provide a relief.

I had to run second to brought up VNC on CentOS 5.2 Dom0
 (on bare metal ASUS P5KR)
I believe Linux driver for Atansic Gigabit Ethernet is not good.
Regarding DomU access from from the Net and vice versa usually
first one helps (at DomU ).
I don't know what exactly Chris did. "gso" option fails.
Some network education is obviously required for myself at least ;)
To read and understand tcpdump's captured logs for instance.


--- On Sat, 4/25/09, Venefax <venefax@xxxxxxxxx> wrote:
From: Venefax <venefax@xxxxxxxxx>
Subject: RE: [Xen-devel] xen.git branch reorg
To: bderzhavets@xxxxxxxxx, "'Jeremy Fitzhardinge'" <jeremy@xxxxxxxx>, "'Christophe Saout'" <christophe@xxxxxxxx>
Cc: "'Xen-devel'" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "'Ian Campbell'" <Ian.Campbell@xxxxxxxxxx>
Date: Saturday, April 25, 2009, 3:03 AM

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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