Open Stack

Hi list,

I'm working under CentOS 6.4 + Havana + Neutron + OVS + gre.

I'm testing performance for gre.

I have a 10Gb/s NIC for compute Node.

While, the max bandwidth I can get is small then 3Gb/s, even I have enough instances.
I noticed the reason the bandwidth can't reach higher is due to the utilization for one CPU core is already 100%.

So, I want to try if I can get higher bandwidth if I have bigger MTU, because the default MTU = 1500.

But, after I set network_device_mtu=8500 in "/etc/nova/nova.conf", and restart openstack-nova-compute service and re-create a new instance, the MTU for devices is still 1500:

202: qbr053ac004-d6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
    link/ether da:c0:8d:c2:d5:1c brd ff:ff:ff:ff:ff:ff
203: qvo053ac004-d6: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether f6:0b:04:3f:9d:41 brd ff:ff:ff:ff:ff:ff
204: qvb053ac004-d6: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether da:c0:8d:c2:d5:1c brd ff:ff:ff:ff:ff:ff
205: tap053ac004-d6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc htb state UNKNOWN qlen 500
    link/ether fe:18:3e:c2:e9:84 brd ff:ff:ff:ff:ff:ff

Anyone know why is this happen ?
How can I solve it ??

Thanks.
-chen
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