Marcelo Tosatti wrote: > In case the VM stops for whatever reason, the host system is not > supposed to adjust time related hardware state to compensate, in an > attempt to present apparent continuous time. > > If you save a VM and then restore it later, it is the guest > responsability to adjust its time representation. If the guest doesn't know it's been stopped, then its time representation will be wrong until it finds out, e.g. after a few minutes with NTP, or even a seconds can be too long. That is sad when it happens because it breaks the coherence of any timed-lease caching the guest is involved in. I.e. where the guest acquires a lock on some data object (like a file in NFS) that it can efficiently access without network round trips (similar to MESI), with all nodes having agreed that it's coherent for, say, 5 seconds before renewing or breaking. (It's just a way to reduce latency.) But we can't trust CLOCK_MONOTONIC when a VM is involved, it's just one of those facts of life. So instead the effort is to try and detect when a VM is involved and then distrust the clock. (Non-VM) suspend/resume is similar, but there's usually a way to be notified about that as it happens. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
