libvirt users - Feb 2017 - How to pin an libvirt lxc to a specific physical CPU core in openstack?

Dear all,

In my applications, the real-time performance is very important, so I used 4
containers, with only one application running in each container and a physical
CPU core is only dedicated to one lxc. and I must know which container is hosted
by which CPU core. That is, I need to pin a specific lxc to a specific CPU core.

I can achieve this in a native linux system by the following xml script (to pin
a libvirt lxc to core #3 of a machine). It works fine.

<vcpu placement='static' cpuset='3'>1</vcpu>


Now I want to realize this on openstack platform, I carefully read the
instruction on CPU pinning in nova and found that openstack flavor can only
support pinning an lxc(instance) onto a set of CPU cores. I cannot allocate a
specific pCPU to an lxc. After the lxc is started, "dumpxml" only
shows the following statement, I even don't know to which CPU core the lxc
is pinned.

<vcpu placement='static' >1</vcpu>

I tried to edit the libvirt.xml for the lxc which locates at
nova/instances/#INSTANCE ID#/libvirt.xml and manually inserted
cpuset='3', but this didn't take effect. After the lxc is restarted,
the libvirt.xml is recovered and the modification was not there anymore.

I googled the question on Internet, but no solution was found. I hope the
libvirt people can help me on this.

Thank you in advance.
Cheng