[ovs-discuss] Poor GRE performance - maybe due to using ip_gre kernel module ?

[D3c3 Balus]

Indeed, I managed to get very good results after I disabled TSO on the gre_sys interface.
As a curiosity, disabling all 3 (TSO, GSO and GRO) on gre_sys interface returned good performance but half the best performance (obtained when only TSO is off).
FYI: LRO was off by default for me.

Thanks everybody !

> On Jul 5, 2016, at 4:45 PM, Alexander Duyck <alexander.duyck at gmail.com> wrote:
> 
> On Mon, Jul 4, 2016 at 1:34 PM, D3c3 Balus <d3c3balus at gmail.com> wrote:
>> Hello,
>> 
>> I’m using 2 Ubuntu Xenial 16.04 LTS with the following:
>> - kernel:  4.4.0-28-generic
>> - OVS version:  2.5.0  (installed from ubuntu packages: openvswitch-common & openvswitch-switch)
>> 
>> I’m configuring a GRE tunnel between OVS bridges running on each of the machines with:
>> 
>> ovs-vsctl add-port br0 tun0 -- set Interface tun0 type=gre options:remote_ip=x.x.x.x
>> 
>> and I achieve connectivity between VMs, as desired, via the GRE tunnel.
>> 
>> 
>> Problem:  iperf test show really low performance (734 bits/sec !!) considering a baseline that shows  almost 1G over the direct link.
>> 
>> Troubleshooting performed:
>> 1. increased MTU of the physical link on both sides: `ip link set dev enp0s8 mtu 2000`  => same poor perf
>> 2. increased MTU of the br0 on both OVS bridges: `ip link set dev br0 mtu 1700`  => same poor perf
>> 
>> [FYI:   I performed the same operations on an older version of Ubuntu = Trusty 14.04 LTS, kernel 3.13.0-86, and after adjusting the MTU as above, the GRE performance was satisfactory ~ 414 Mbps !! ]
> 
> One data point that would be really useful would be what physical
> links are you using, specifically what driver and device combination.
> More often then not these type of issues are due to something like LRO
> or GRO creating an oversized frame, or the TSO feature advertising
> support for a tunnel it doesn't actually support.  You might go
> through and verify if any of these features are enabled on the
> physical link using "ethtool -k" and then go through and disable them
> until you see the performance improve.
> 
> Hope that helps.
> 
> - Alex