CPU pinning implementation through libvirt

[xtec]

I'll be direct.

After learning that QEMU itself has never officially implemented options 
such as "-vcpu", "-vcpupin", or similar, remaining only as unimplemented 
commits at their mailing lists, I felt the need of asking here once and 
for all:

How does libvirt actually implements CPU pinning under the hood?
There's the xml with the cputune section and all the vcpupins, but does 
libvirt translates this to QEMU native commands, or what else does it 
do?

Thanks.