FYI, to make this work you need to have cgroups mounted.

eg, 

   mkdir /dev/cgroup
   mount -t cgroup none -o cpu,devices /dev/cgroup


And then restart libvirtd, and restart any guests and it should work.

I am closing this as notabug . This works fine when kernel cgroups are utilized correctly. 

[root@dell-pe1955-01 ~]# virsh schedinfo F11_gold_x86_64
Scheduler      : posix
cpu_shares     : 1024

[root@dell-pe1955-01 ~]# virsh schedinfo --set cpu_shares=2048 F11_gold_x86_64
Scheduler      : posix
cpu_shares     : 2048

[root@dell-pe1955-01 ~]# virsh schedinfo F11_gold_x86_64
Scheduler      : posix
cpu_shares     : 2048