[Openstack] Directional network performance issues with Neutron + OpenvSwitch

Martinx - ジェームズ thiagocmartinsc at gmail.com
Fri Oct 25 14:13:47 UTC 2013

Hi Darragh,

Yes, Instances are getting MTU 1400.

I'm using LibvirtHybridOVSBridgeDriver at my Compute Nodes. I'll check BG
1223267 right now!

The LibvirtOpenVswitchDriver doesn't work, look:



My NICs are "RTL8111/8168/8411 PCI Express Gigabit Ethernet", Hypervisors
motherboard are MSI-890FXA-GD70.

The command "ethtool -K eth1 gro off" did not had any effect on the
communication between instances on different hypervisors, still poor,
around 248Mbit/sec, when its physical path reach 1Gbit/s (where GRE is

My Linux version is "Linux hypervisor-1 3.8.0-32-generic
#47~precise1-Ubuntu", same kernel on Network Node" and others nodes too
(Ubuntu 12.04.3 installed from scratch for this Havana deployment).

The only difference I can see right now, between my two hypervisors, is
that my second is just a spare machine, with a slow CPU but, I don't think
it will have a negative impact at the network throughput, since I have only
1 Instance running into it (plus a qemu-nbd process eating 90% of its CPU).
I'll replace this CPU tomorrow, to redo this tests again but, I don't think
that this is the source of my problem. The MOBOs of two hypervisors
are identical, 1 3Com (manageable) switch connecting the two.


On 25 October 2013 07:15, Darragh O'Reilly <dara2002-openstack at yahoo.com>wrote:

> Hi Thiago,
> you have configured DHCP to push out a MTU of 1400. Can you confirm that
> the 1400 MTU is actually getting out to the instances by running 'ip link'
> on them?
> There is an open problem where the veth used to connect the OVS and Linux
> bridges causes a performance drop on some kernels -
> https://bugs.launchpad.net/nova-project/+bug/1223267 .  If you are using
> the LibvirtHybridOVSBridgeDriver VIF driver, can you try changing to
> LibvirtOpenVswitchDriver and repeat the iperf test between instances on
> different compute-nodes.
> What NICs (maker+model) are you using? You could try disabling any
> off-load functionality - 'ethtool -k <iface-used-for-gre>'.
> What kernal are you using: 'uname -a'?
> Re, Darragh.
> > Hi Daniel,
> >
> > I followed that page, my Instances MTU is lowered by DHCP Agent but, same
> > result: poor network performance (internal between Instances and when
> > trying to reach the Internet).
> >
> > No matter if I use
> "dnsmasq_config_file=/etc/neutron/dnsmasq-neutron.conf +
> > "dhcp-option-force=26,1400"" for my Neutron DHCP agent, or not (i.e. MTU
> =
> > 1500), the result is almost the same.
> >
> > I'll try VXLAN (or just VLANs) this weekend to see if I can get better
> > results...
> >
> > Thanks!
> > Thiago
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