Re: [Xen-devel] [PATCH v3 04/13] x86/time.c: Scale host TSC in pvclock properly

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/30/2015 10:03 PM, Haozhong Zhang wrote:
> This patch makes the pvclock return the scaled host TSC and
> corresponding scaling parameters to HVM domains if guest TSC is not
> emulated and TSC scaling is enabled.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> ---
> Changes in v3:
>   (addressing Boris Ostrovsky's comments)
>   * No changes in fact. tsc_set_info() does not set d->arch.vtsc to 0
>     if host_tsc_is_safe() is not satisfied, so it is safe to use
>     d->arch.vtsc_to_ns here.
I don't think I understand your argument here. I think last time we 
decided that vtsc_to_ns can be used only if TSC is constant.
-boris

>   xen/arch/x86/time.c | 16 ++++++++++++----
>   1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index d83f068..b31634a 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -815,10 +815,18 @@ static void __update_vcpu_system_time(struct vcpu *v, int 
> force)
>       }
>       else
>       {
> -        tsc_stamp = t->local_tsc_stamp;
> -
> -        _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
> -        _u.tsc_shift         = (s8)t->tsc_scale.shift;
> +        if ( has_hvm_container_domain(d) && cpu_has_tsc_ratio )
> +        {
> +            tsc_stamp            = hvm_funcs.scale_tsc(v, t->local_tsc_stamp);
> +            _u.tsc_to_system_mul = d->arch.vtsc_to_ns.mul_frac;
> +            _u.tsc_shift         = d->arch.vtsc_to_ns.shift;
> +        }
> +        else
> +        {
> +            tsc_stamp            = t->local_tsc_stamp;
> +            _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
> +            _u.tsc_shift         = (s8)t->tsc_scale.shift;
> +        }
>       }
>   
>       _u.tsc_timestamp = tsc_stamp;

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