My understanding is one of the reasons that the virtual time stuff in clouds doesn't work in a straightforward way is that your VM can migrate to another host, where reading TSC could give the appearance of discontinuous time, including jumping backwards in time which would be very bad. This is not a problem unless your VMs are migratory, which I guess is something I associate with GCE. And clouds seem to me to have more variety of hardware than I'd expect in my own private infrastructure, and that variety comes with a great many TSC quirks.