Re: Problems with dropped packets on bonded interface for 3.x kernels

[Albert Chin <linux-netdev@mlists.thewrittenword.com>]

On Mon, Nov 21, 2011 at 07:32:03AM +0100, Eric Dumazet wrote:
> Le dimanche 20 novembre 2011 à 23:16 -0600, Albert Chin a écrit :
> > I'm running Ubuntu 11.10 on an Intel SR2625URLXR system with an Intel
> > S5520UR motherboard and an internal Intel E1G44HT (I340-T4) Quad Port
> > Server Adapter. I am seeing dropped packets on a bonded interface,
> > comprised of two GigE ports on the Intel E1G44HT Quad Port Server
> > Adapter. The following kernels exhibit this problem:
> >   3.0.0-12-server, 3.0.0-13-server, 3.1.0-2-server, 3.2.0-rc2
> > Installing Fedora 16 with a 3.1.1-1.fc16.x86_64 also showed dropped
> > packets.
> > 
> > I also tried RHEL6 with a 2.6.32-131.17.1.el6.x86_64 kernel and didn't
> > see any dropped packets. Testing an older 2.6.32-28.55-generic Ubuntu
> > kernel also didn't show any dropped packets.
> > 
> > So, with 2.6, I don't see dropped packets, but everything including
> > 3.0 and after show dropped packets.
> > 
> > # ifconfig bond0
> > bond0     Link encap:Ethernet  HWaddr 00:1b:21:d3:f6:0a  
> >           inet6 addr: fe80::21b:21ff:fed3:f60a/64 Scope:Link
> >           UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1
> >           RX packets:225 errors:0 dropped:186 overruns:0 frame:0
> >           TX packets:231 errors:0 dropped:0 overruns:0 carrier:0
> >           collisions:0 txqueuelen:0 
> >           RX bytes:25450 (25.4 KB)  TX bytes:28368 (28.3 KB)
> > 
> > [[ snip snip ]]
> 
> Old kernels were dropping some packets (unknown protocols...) without
> counting them.
> 
> So following patch was added in 2.6.37 :
> 
> You could use tcdpump to identify what are these dropped packets :)

So only "unknown" protocols are dropped? I just ran tcpdump for 96
packets and inspected the output. The only packets received are LACP,
ARP, STP (Spanning Tree Protocol), DTP (Dynamic Trunking Protocol).
How are these "unknown"?

> commit caf586e5f23cebb2a68cbaf288d59dbbf2d74052
> Author: Eric Dumazet <eric.dumazet@gmail.com>
> Date:   Thu Sep 30 21:06:55 2010 +0000
> 
>     net: add a core netdev->rx_dropped counter
>     
>     In various situations, a device provides a packet to our stack and we
>     drop it before it enters protocol stack :
>     - softnet backlog full (accounted in /proc/net/softnet_stat)
>     - bad vlan tag (not accounted)
>     - unknown/unregistered protocol (not accounted)
>     
>     We can handle a per-device counter of such dropped frames at core level,
>     and automatically adds it to the device provided stats (rx_dropped), so
>     that standard tools can be used (ifconfig, ip link, cat /proc/net/dev)
>     
>     This is a generalization of commit 8990f468a (net: rx_dropped
>     accounting), thus reverting it.
>     
>     Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
>     Signed-off-by: David S. Miller <davem@davemloft.net>

-- 
albert chin (china@thewrittenword.com)