On Wed, Feb 26, 2014 at 07:15:12PM +0100, Andrew Jones wrote:
> commit 0061d53daf26f introduced a mechanism to execute a global clock
> update for a vm. We can apply this periodically in order to propagate
> host NTP corrections. Also, if all vcpus of a vm are pinned, then
> without an additional trigger, no guest NTP corrections can propagate
> either, as the current trigger is only vcpu cpu migration.
>
> Signed-off-by: Andrew Jones <drjo...@redhat.com>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/x86.c | 65
> +++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 63 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 9aa09d330a4b5..77c69aa4756f9 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -599,6 +599,7 @@ struct kvm_arch {
> u64 master_kernel_ns;
> cycle_t master_cycle_now;
> struct delayed_work kvmclock_update_work;
> + bool clocks_synced;
>
> struct kvm_xen_hvm_config xen_hvm_config;
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a2d30de597b7d..5cba20b446aac 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1620,6 +1620,60 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> return 0;
> }
>
> +static void kvm_schedule_kvmclock_update(struct kvm *kvm, bool now);
> +static void clock_sync_fn(struct work_struct *work);
> +static DECLARE_DELAYED_WORK(clock_sync_work, clock_sync_fn);
> +
> +#define CLOCK_SYNC_PERIOD_SECS 300
> +#define CLOCK_SYNC_BUMP_SECS 30
> +#define CLOCK_SYNC_STEP_MSECS 100
> +
> +#define __steps(s) (((s) * MSEC_PER_SEC) / CLOCK_SYNC_STEP_MSECS)
> +
> +static void clock_sync_fn(struct work_struct *work)
> +{
> + static unsigned reset_step = __steps(CLOCK_SYNC_PERIOD_SECS);
> + static unsigned step = 0;
> + struct kvm *kvm;
> + bool sync = false;
> +
> + spin_lock(&kvm_lock);
Better have it per vm to avoid kvm_lock?
> + if (step == 0)
> + list_for_each_entry(kvm, &vm_list, vm_list)
> + kvm->arch.clocks_synced = false;
> +
> + list_for_each_entry(kvm, &vm_list, vm_list) {
> + if (!kvm->arch.clocks_synced) {
> + kvm_get_kvm(kvm);
> + sync = true;
> + break;
> + }
> + }
> +
> + spin_unlock(&kvm_lock);
> +
> + if (sync) {
> + kvm_schedule_kvmclock_update(kvm, true);
> + kvm_put_kvm(kvm);
> +
> + if (++step == reset_step) {
> + reset_step += __steps(CLOCK_SYNC_BUMP_SECS);
> + pr_warn("kvmclock: reducing VM clock sync frequency "
> + "to every %ld seconds.\n", (reset_step
> + * CLOCK_SYNC_STEP_MSECS)/MSEC_PER_SEC);
> + }
Can you explain the variable sync frequency? To be based on NTP
frequency correction?
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