diff options
author | Avi Kivity <avi@qumranet.com> | 2008-03-04 03:44:51 -0500 |
---|---|---|
committer | Avi Kivity <avi@qumranet.com> | 2008-04-27 04:53:27 -0400 |
commit | 019960ae9933161c2809fa4ee608ba30d9639fd2 (patch) | |
tree | c4ded864dfd339a2c64451220d0866eba854b63c /arch/x86/kvm | |
parent | b8688d51bbe4872fbcec751e04369606082ac610 (diff) |
KVM: VMX: Don't adjust tsc offset forward
Most Intel hosts have a stable tsc, and playing with the offset only
reduces accuracy. By limiting tsc offset adjustment only to forward updates,
we effectively disable tsc offset adjustment on these hosts.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r-- | arch/x86/kvm/vmx.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 7ef710afceba..fb0389d3a8d1 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c | |||
@@ -519,7 +519,7 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) | |||
519 | { | 519 | { |
520 | struct vcpu_vmx *vmx = to_vmx(vcpu); | 520 | struct vcpu_vmx *vmx = to_vmx(vcpu); |
521 | u64 phys_addr = __pa(vmx->vmcs); | 521 | u64 phys_addr = __pa(vmx->vmcs); |
522 | u64 tsc_this, delta; | 522 | u64 tsc_this, delta, new_offset; |
523 | 523 | ||
524 | if (vcpu->cpu != cpu) { | 524 | if (vcpu->cpu != cpu) { |
525 | vcpu_clear(vmx); | 525 | vcpu_clear(vmx); |
@@ -559,8 +559,11 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) | |||
559 | * Make sure the time stamp counter is monotonous. | 559 | * Make sure the time stamp counter is monotonous. |
560 | */ | 560 | */ |
561 | rdtscll(tsc_this); | 561 | rdtscll(tsc_this); |
562 | delta = vcpu->arch.host_tsc - tsc_this; | 562 | if (tsc_this < vcpu->arch.host_tsc) { |
563 | vmcs_write64(TSC_OFFSET, vmcs_read64(TSC_OFFSET) + delta); | 563 | delta = vcpu->arch.host_tsc - tsc_this; |
564 | new_offset = vmcs_read64(TSC_OFFSET) + delta; | ||
565 | vmcs_write64(TSC_OFFSET, new_offset); | ||
566 | } | ||
564 | } | 567 | } |
565 | } | 568 | } |
566 | 569 | ||