Re: [Xen-devel] [PATCH 09/13] x86/time.c: Scale host TSC in pvclock properly

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/28/2015 03:13 AM, 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>
> ---
>   xen/arch/x86/time.c | 15 ++++++++++++---
>   1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index 4b5402c..54eab6e 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -832,10 +832,19 @@ static void __update_vcpu_system_time(struct vcpu *v, int 
> force)
>       }
>       else
>       {
> -        _u.tsc_timestamp     = t->local_tsc_stamp;
> +        if ( is_hvm_domain(d) && hvm_funcs.tsc_scaling_supported )
> +        {
> +            _u.tsc_timestamp     = hvm_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
> +        {
> +            _u.tsc_timestamp     = t->local_tsc_stamp;
> +            _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
> +            _u.tsc_shift         = (s8)t->tsc_scale.shift;
> +        }
>           _u.system_time       = t->stime_local_stamp;
> -        _u.tsc_to_system_mul = t->tsc_scale.mul_frac;
> -        _u.tsc_shift         = (s8)t->tsc_scale.shift;
>       }
>       if ( is_hvm_domain(d) )
>           _u.tsc_timestamp += v->arch.hvm_vcpu.cache_tsc_offset;
So this is not directly related to this series but when we calculate 
tsc_timestamp --- shouldn't we subtract TSC offset? Otherwise we are 
reporting (possibly scaled) host's TSC and this is supposed to be 
guest's counter.

-boris

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel