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SubjectRe: [PATCH 2/4] KVM: x86: rewrite handling of scaled TSC for kvmclock
On Mon, Feb 08, 2016 at 04:18:29PM +0100, Paolo Bonzini wrote:
> This is the same as before:
>
> kvm_scale_tsc(tgt_tsc_khz)
> = tgt_tsc_khz * ratio
> = tgt_tsc_khz * user_tsc_khz / tsc_khz (see set_tsc_khz)
> = user_tsc_khz (see kvm_guest_time_update)
> = vcpu->arch.virtual_tsc_khz (see kvm_set_tsc_khz)
>
> However, computing it through kvm_scale_tsc makes it possible
> to include the NTP correction in tgt_tsc_khz, as done in the
> next patch.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/x86.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1ca2b44f70bb..6db3c219795b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1713,7 +1713,7 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
>
> static int kvm_guest_time_update(struct kvm_vcpu *v)
> {
> - unsigned long flags, this_tsc_khz, tgt_tsc_khz;
> + unsigned long flags, tgt_tsc_khz;
> struct kvm_vcpu_arch *vcpu = &v->arch;
> struct kvm_arch *ka = &v->kvm->arch;
> s64 kernel_ns;
> @@ -1739,8 +1739,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>
> /* Keep irq disabled to prevent changes to the clock */
> local_irq_save(flags);
> - this_tsc_khz = __this_cpu_read(cpu_tsc_khz);
> - if (unlikely(this_tsc_khz == 0)) {
> + tgt_tsc_khz = __this_cpu_read(cpu_tsc_khz);
> + if (unlikely(tgt_tsc_khz == 0)) {
> local_irq_restore(flags);
> kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
> return 1;
> @@ -1775,13 +1775,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
> if (!vcpu->pv_time_enabled)
> return 0;
>
> - if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {
> - tgt_tsc_khz = kvm_has_tsc_control ?
> - vcpu->virtual_tsc_khz : this_tsc_khz;
> + if (kvm_has_tsc_control)
> + tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz);
> +
> + if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) {
> kvm_get_time_scale(NSEC_PER_SEC / 1000, tgt_tsc_khz,
> &vcpu->hv_clock.tsc_shift,
> &vcpu->hv_clock.tsc_to_system_mul);
> - vcpu->hw_tsc_khz = this_tsc_khz;
> + vcpu->hw_tsc_khz = tgt_tsc_khz;
> }
>
> /* With all the info we got, fill in the values */
> --
> 1.8.3.1
>

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>

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