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
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