In past versions I think it was global BIG-IP CPU for the unit the VS was on. Since we added per-LTM VS CPU metrics in 11.1 it could potentially be per VS for the GTM metric now. You could open a case with F5 Support to confirm/correct this. If it's not per-LTM VS CPU metrics in 11.1, you could ask to have a request for enhancement opened. If you do, ask Support to reference BZ216992 for some background info.
The Kb/sec mode could be per VS as that's been available for a while.
The communication between GTM and LTM is performed over iQuery.
Aaron