On 20/08/21 14:46, Marcelo Tosatti wrote:
On Mon, Aug 16, 2021 at 12:11:27AM +0000, Oliver Upton wrote:
Handling the migration of TSCs correctly is difficult, in part because
Linux does not provide userspace with the ability to retrieve a (TSC,
realtime) clock pair for a single instant in time. In lieu of a more
convenient facility, KVM can report similar information in the kvm_clock
structure.
Provide userspace with a host TSC & realtime pair iff the realtime clock
is based on the TSC. If userspace provides KVM_SET_CLOCK with a valid
realtime value, advance the KVM clock by the amount of elapsed time. Do
not step the KVM clock backwards, though, as it is a monotonic
oscillator.
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
This is a good idea. Userspace could check if host and destination
clocks are up to a certain difference and not use the feature if
not appropriate.
Is there a qemu patch for it?
Not yet, but Maxim had a patch for a similar series (though with a
different userspace API).
Paolo
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