On 10/6/25 16:41, Pavel Hrdina wrote: > 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
Ah, very good catch! Let's keep it under timers and fix our docs. I'll post v2 soon. Michal
