looking for info on TSC virtualization with kvm

looking for info on TSC virtualization with kvm

[Chris Friesen]

I'm trying to find out some hard data on TSC virtualization when using 
qemu-kvm to run linux guests on Intel-based linux 3.4 hosts.

I've read 
"https://www.kernel.org/doc/Documentation/virtual/kvm/timekeeping.txt" 
and looked at the code somewhat, but it's a bit tricky to figure out 
exactly what will happen.

I'm using kvm_clock for the guest kernel clocksource, but I'm concerned 
about applications in the guest accessing the TSC directly.

My main concern is what happens during live migration to a host with a 
faster TSC frequency (even though both hosts may have nonstop constant 
TSCs).

It appears that VMX provides hardware virtualization of the TSC to allow 
an offset to be applied, but no support for frequency scaling.  Under 
what circumstances would KVM use the hardware virtualized TSC?  What 
would happen on migration to a host with faster TSC?

Does KVM support a fully-emulated software TSC?  If so, under what 
circumstances would it be used and can it handle frequency shifts and 
offsets over live migration?

Lastly...I found a patch series by Zachary Amsden at 
"http://thread.gmane.org/gmane.linux.kernel/1157689" that doesn't seem 
to have ever made it in to the mainline kernel...why not?

Thanks,
Chris