From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v3 04/13] x86/time.c: Scale host TSC in
	pvclock properly
Date: Mon, 4 Jan 2016 13:09:57 -0500
Message-ID: <568AB575.7090608@oracle.com>
References: <1451531020-29964-1-git-send-email-haozhong.zhang@intel.com>
	<1451531020-29964-5-git-send-email-haozhong.zhang@intel.com>
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To: Haozhong Zhang <haozhong.zhang@intel.com>, xen-devel@lists.xen.org, Jan Beulich <jbeulich@suse.com>, Kevin Tian <kevin.tian@intel.com>
Cc: Jun Nakajima <jun.nakajima@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Keir Fraser <keir@xen.org>, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
List-Id: xen-devel@lists.xenproject.org

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@intel.com>
> ---
> 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;