On Mon, Oct 06, 2025 at 03:14:46PM +0200, Michal Privoznik via Devel wrote: > From: Michal Privoznik <[email protected]> > > QEMU supports this enlightenment since version 2.0. It's required > by some other enlightenments (e.g. hv-stimer, hv-stimer-direct). > >From QEMU docs: > > ``hv-time`` > Enables two Hyper-V-specific clocksources available to the guest: MSR-based > Hyper-V clocksource (HV_X64_MSR_TIME_REF_COUNT, 0x40000020) and Reference > TSC > page (enabled via MSR HV_X64_MSR_REFERENCE_TSC, 0x40000021). Both > clocksources > are per-guest, Reference TSC page clocksource allows for exit-less time > stamp > readings. Using this enlightenment leads to significant speedup of all > timestamp > related operations.
We already support this feature but not via hyper-v specific element, it's hidden in timers <https://libvirt.org/formatdomain.html#time-keeping> by using `hypervclock` timer. See VIR_DOMAIN_TIMER_NAME_HYPERVCLOCK in libvirt code. If we want to introduce it in hyper-v features as well we need to make sure these two places in XML reflect the correct state. It also seems that our timer documentation is wrong as it states that the `hypervclock` timer is available since QEMU 1.2.2 . Pavel
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