On Tue, 2026-05-26 at 14:57 +0100, David Woodhouse wrote: > > One simple option that occurs to me would be to add a 'cycles_raw' > value to the system_time_snapshot, for PV clocksources like hyperv and > kvmclock to populate with the original TSC reading. > > That might actually let us clean up some of the PTP code that currently > has to deal with TSC vs. kvmclock in counter snapshots too. I think I > could kill the use of get_cycles() in vmclock for the kvmclock case, > which might make Thomas happy...
I hacked that up to see what it looks like, and it kind of seems to work... Based on merging my kvmclock branch and Thomas's ktime_get_snapshot_id(): • https://git.infradead.org/?p=users/dwmw2/linux.git;a=shortlog;h=refs/heads/kvmclock5 • https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/log/?h=timers/ptp/timekeeping I'll probably not post this for real until the above two are merged; there's no rush but I think it's a worthwhile cleanup. For now it's at • https://git.infradead.org/?p=users/dwmw2/linux.git;a=shortlog;h=refs/heads/kvm-ktime-snapshot David Woodhouse (8): timekeeping: Add clocksource read_raw() method and raw_cycles to snapshot clocksource/hyperv: Implement read_raw() for TSC page clocksource x86/kvmclock: Implement read_raw() for kvmclock clocksource KVM: x86: Use ktime_get_snapshot_id() for master clock KVM: x86: Compute kvmclock base without pvclock_gtod_data KVM: x86: Replace pvclock_gtod_data vclock_mode with boolean KVM: x86: Remove pvclock_gtod_data and private timekeeping code ptp: vmclock: Use raw_cycles from snapshot for precise TSC pairing arch/x86/kernel/kvmclock.c | 21 ++++ arch/x86/kvm/x86.c | 239 ++++++++----------------------------- drivers/clocksource/hyperv_timer.c | 14 +++ drivers/ptp/ptp_vmclock.c | 4 + include/linux/clocksource.h | 8 ++ include/linux/timekeeping.h | 6 + kernel/time/timekeeping.c | 30 ++++- 7 files changed, 130 insertions(+), 192 deletions(-)
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