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SubjectRe: [PATCH 0/4] kvmclock: improve accuracy
On Mon, Feb 08, 2016 at 04:18:27PM +0100, Paolo Bonzini wrote:
> Currently kvmclock is obtaining the multiplier and shift value from
> the TSC kHz. These however are less accurate than the host kernel's
> clock, which includes corrections made through NTP.
>
> These patches change kvmclock to tick at the same frequency as the
> host kernel's clocksource (as obtained through the pvclock_gtod
> notifier). This is precise enough that the Hyper-V clock can be
> implemented on top of it.

Note the current option to sync kvmclock periodically every 300 seconds:

#define KVMCLOCK_SYNC_PERIOD (300 * HZ)

static void kvmclock_sync_fn(struct work_struct *work)
{
struct delayed_work *dwork = to_delayed_work(work);
struct kvm_arch *ka = container_of(dwork, struct kvm_arch,
kvmclock_sync_work);
struct kvm *kvm = container_of(ka, struct kvm, arch);

schedule_delayed_work(&kvm->arch.kvmclock_update_work, 0);
schedule_delayed_work(&kvm->arch.kvmclock_sync_work,
KVMCLOCK_SYNC_PERIOD);
}

How large is the error when the corrections are applied every 5 minutes?

Does this match the errors you are seeing?


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