diff options
| author | Avi Kivity <avi@qumranet.com> | 2008-03-04 10:44:51 +0200 |
|---|---|---|
| committer | Avi Kivity <avi@qumranet.com> | 2008-04-27 11:53:27 +0300 |
| commit | 019960ae9933161c2809fa4ee608ba30d9639fd2 (patch) | |
| tree | c4ded864dfd339a2c64451220d0866eba854b63c | |
| 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>
| -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 7ef710afceb..fb0389d3a8d 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) { struct vcpu_vmx *vmx = to_vmx(vcpu); u64 phys_addr = __pa(vmx->vmcs); - u64 tsc_this, delta; + u64 tsc_this, delta, new_offset; if (vcpu->cpu != cpu) { vcpu_clear(vmx); @@ -559,8 +559,11 @@ static void vmx_vcpu_load(struct kvm_vcpu *vcpu, int cpu) * Make sure the time stamp counter is monotonous. */ rdtscll(tsc_this); - delta = vcpu->arch.host_tsc - tsc_this; - vmcs_write64(TSC_OFFSET, vmcs_read64(TSC_OFFSET) + delta); + if (tsc_this < vcpu->arch.host_tsc) { + delta = vcpu->arch.host_tsc - tsc_this; + new_offset = vmcs_read64(TSC_OFFSET) + delta; + vmcs_write64(TSC_OFFSET, new_offset); + } } } |