netdev - Re: PROBLEM: Bnx2x Checksum/Length Error Over GRE Tunnel

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Date:	Tue, 03 Feb 2015 10:46:36 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eren Türkay <erent@...atlas.com>
Cc:	Network Development <netdev@...r.kernel.org>
Subject: Re: PROBLEM: Bnx2x Checksum/Length Error Over GRE Tunnel

On Tue, 2015-02-03 at 20:05 +0200, Eren Türkay wrote:
> Hello,
> 
> I am having incorrect checksum and length calculation error when using
> GRE tunnel and this leads to unstable/unreliable connections where even
> simple nc connection cannot be made correctly due to a lot of TCP
> retransmissions. The reported iperf output becomes 23Kbit/s.
> 
> When I disable tx checksumming with "ethtool -K eth0 tx off", the
> problem seems to be solved but then I lose tcp segmentation offloading
> support, without which adds an additional overhead on 10Gbit network
> interface. With tx off, I get 4 to 7Gbit/s with parallel 40 connections
> using iperf.
> 
> In tcpdump output (tcpdump -i em1 proto gre) when tx checksumming is
> enabled, I see "checksum error" in every packet + "IP truncated-ip -
> 63631 bytes missing!" messages, and a lot of TCP
> retransmissions. When tx is off, checksums are correct but I get 4-7Gbit
> output. With GSO generalization code in [0] it is reported that
> 9.3Gbit/s is possible over GRE tunnel but I'm nowhere near these results.

Strange, I am using bnx2x with no such problem.

Please note that tcpdump can display "checksum error" because it doesn't
always know the NIC will generate the checksums.

Can you please send : ifconfig -a, as I suspect an MTU issue

Here I easily reach line rate with a single flow.

ip tunnel add gre1 mode gre remote 10.246.11.52 local 10.246.11.51
ip link set gre1 up
ip addr add 7.7.8.51/24 dev gre1


lpk51:~# ip ro get 7.7.8.52
7.7.8.52 dev gre1  src 7.7.8.51 
    cache  expires 557sec mtu 1476

lpk51:~# ./netperf -H 7.7.8.52 -Cc
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.52 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  16384  16384    10.00      9227.94   2.52     3.96     0.715   1.125  



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