Thanks for your help, Blair!
Yes, I added NUMA information into libvirt domain xml (libvirtd 1.2.8 / CentOS7.1).
In case of 4KB mpirun using 40G Ethernet, the result pattern is as follows:
* hostA<->hostB (3797.05 MB/s)
* hostA<->hostB's VM (3521.03 MB/s)
* hostA's VM<->hostB's VM (830.20 MB/s)