4.4 use gre tunnel failed

[cloud]

Hi all, When I use 4.4 GRE to isolate guest network, and cloudbr1 as the guest 
bridge, other traffic types on cloudbr0,
When I try to create vm, there is an exception as below. Isn't it the OVS 
controller auto creat OVSTunnel316 ?
And another question: is it no need to set SDN controller enable in global 
configuration, cause I only see the
"
| sdn.ovs.controller.default.label |
"
which I have set to cloudbr1

2014-07-23 15:38:40,420 WARN  [kvm.resource.LibvirtComputingResource] 
(agentRequest-Handler-1:null) LibvirtException  
org.libvirt.LibvirtException: Cannot get interface MTU on 'OVSTunnel316': no 
such device                             
        at org.libvirt.ErrorHandler.processError(Unknown Source)                
                                      
        at org.libvirt.Connect.processError(Unknown Source)                     
                                      
        at org.libvirt.Connect.processError(Unknown Source)                     
                                      
        at org.libvirt.Connect.domainCreateXML(Unknown Source)                  
                                      

        at 
com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.startVM(LibvirtComputingResource.java:1239)
 


Thanks