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

[D3c3 Balus]

Small update:  I have installed the latest OVS from git master  (following this https://github.com/openvswitch/ovs/blob/master/INSTALL.Debian.md <https://github.com/openvswitch/ovs/blob/master/INSTALL.Debian.md> - option 2: build packages -> then installed openvswitch-datapath-dkms). 
After increasing the MTU on the physical link between the boxes / hypervisors, the iperf tests are still very bad:   3.21 Mbits/sec

Thanks,

DC



> On Jul 4, 2016, at 9:34 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 !! ]
> 
> I continued troubleshooting my Ubuntu Xenial 16.04 (kernel 4.4.0-28):
> 3. I noticed that this system has these interfaces gre0 at NONE, gretap0 at NONE, gre_sys at NONE  (which did not appear on Ubuntu Trusty 14.04, kernel 3.13.0-86) and realized that Ubuntu Xenial 16.04 uses the linux kernel module ip_gre instead of the one provided by Open vSwitch:
> 
> SNAPSHOT from Ubuntu Xenial 16.04 (kernel 4.4.0-28):
> ```
> root at xenial ~$ lsmod | grep gre
> vport_gre              16384  1
> ip_gre                 20480  1 vport_gre
> ip_tunnel              28672  1 ip_gre
> gre                    16384  1 ip_gre
> openvswitch            98304  3 vport_gre
> 
> root at xenial ~$ dmesg | grep gre
> ..
> [  379.947836] gre: GRE over IPv4 demultiplexor driver
> [  379.955295] ip_gre: GRE over IPv4 tunneling driver
> [  379.960352] device gre_sys entered promiscuous mode
> ```
> 
> SNAPSHOT from Ubuntu Trusty (kernel 3.13.0-86):
> ```
> root at trusty ~$ lsmod | grep gre
> gre                    13796  1 openvswitch
> 
> root at trusty ~$ dmesg | grep gre
> [    9.270743] gre: GRE over IPv4 demultiplexor driver
> root at box-0 ~$
> ```
> 
> 3. It seems that latest OVS version uses vport_gre kernel module for GRE and this one depends on Linux GRE module (ip_gre):
> 
> ```
> root at xenial ~$ modinfo vport_gre
> filename:       /lib/modules/4.4.0-28-generic/kernel/net/openvswitch/vport-gre.ko
> alias:          vport-type-3
> license:        GPL
> description:    OVS: GRE switching port
> srcversion:     A4455AB407AE7569E81E791
> depends:        openvswitch,ip_gre
> intree:         Y
> vermagic:       4.4.0-28-generic SMP mod_unload modversions
> ```
> 
> 
> 
> Questions:
> 1.  is this intended - that the latest versions of OVS uses the linux GRE module (instead of its own, as it seem it was the case in the past)?
> 2. I tried stopping OVS and unloading the Linux GRE module - but that was unsuccessful.  How should I fix my problem in order to achieve satisfactory level of performance over GRE ?
> 
> 
> Thank you,
> 
> 
> DC

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