Subject: Re: [Lxc-users] Bad checksums and lost packets with macvlan on dummy

From: Daniel Lezcano <[email-masked]>
Date: Sun, 27 Feb 2011 16:14:39 +0100

On 02/23/2011 06:13 PM, Andrian Nord wrote:
> On Mon, Feb 21, 2011 at 05:07:31PM +0100, Daniel Lezcano wrote:
>> I Cc'ed the netdev mailing list and Patrick in case my analysis is wrong
>> or incomplete.
> I'm confirming, that this happens only when macvlan's are onto dummy net
> device. In case of some physical interface under macvlan there is no lost
> packages and no broken checksums.

I did some tests with a 2.6.35 kernel version and it seems the checksum 
errors do not appear.
I noticed there are some changes in the dummy setup function:

   dev->features   |= NETIF_F_SG | NETIF_F_FRAGLIST | NETIF_F_TSO;
   dev->features   |= NETIF_F_NO_CSUM | NETIF_F_HIGHDMA | NETIF_F_LLTX;

May be that was introduced by commit:

commit 6d81f41c58c69ddde497e9e640ba5805aa26e78c
Author: Eric Dumazet <[email-masked]>
Date:   Mon Sep 27 20:50:33 2010 +0000

     dummy: percpu stats and lockless xmit

     Converts dummy network device driver to :

     - percpu stats

     - 64bit stats

     - lockless xmit (NETIF_F_LLTX)

     - performance features added (NETIF_F_SG | NETIF_F_FRAGLIST |
     NETIF_F_TSO | NETIF_F_NO_CSUM | NETIF_F_HIGHDMA)

     Signed-off-by: Eric Dumazet <[email-masked]>
     Signed-off-by: David S. Miller <[email-masked]>

Eric,

Andrian is observing, with a couple of macvlan (in bridge mode) on top 
of a dummy interface, a lot of checksums error and packets drop.
Each macvlan is in a different network namespace and the dummy interface 
is in the init_net.

Any ideas ?