Re: [PATCH 16/17] TSC reset compensation

Glauber Costa
2010-06-16T13:52:11Z

On Mon, Jun 14, 2010 at 09:34:18PM -1000, Zachary Amsden wrote:
> Attempt to synchronize TSCs which are reset to the same value. In the
> case of a reliable hardware TSC, we can just re-use the same offset, but
> on non-reliable hardware, we can get closer by adjusting the offset to
> match the elapsed time.
>
> Signed-off-by: Zachary Amsden <zamsden@redhat.com>
> ---
> arch/x86/kvm/x86.c | 34 ++++++++++++++++++++++++++++++++--
> 1 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8e836e9..cedb71f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -937,14 +937,44 @@ static inline void kvm_request_guest_time_update(struct kvm_vcpu *v)
> set_bit(KVM_REQ_CLOCK_SYNC, &v->requests);
> }
>
> +static inline int kvm_tsc_reliable(void)
> +{
> + return (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
> + boot_cpu_has(X86_FEATURE_NONSTOP_TSC) &&
> + !check_tsc_unstable());
> +}
> +
why can't we re-use vmware TSC_RELIABLE flag?