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KVM: x86: rewrite handling of scaled TSC for kvmclock

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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 will make it possible
to include the NTP correction in tgt_tsc_khz.

Reviewed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2016-02-08 14:51:40 +01:00
parent 4941b8cb37
commit 78db6a5037
1 changed files with 8 additions and 7 deletions
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15
arch/x86/kvm/x86.c
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@ -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 */