From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH 09/13] x86/time.c: Scale host TSC in pvclock
	properly
Date: Thu, 22 Oct 2015 11:50:18 -0400
Message-ID: <562905BA.9090709@oracle.com>
References: <1443424438-13404-1-git-send-email-haozhong.zhang@intel.com>
	<1443424438-13404-10-git-send-email-haozhong.zhang@intel.com>
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To: Haozhong Zhang <haozhong.zhang@intel.com>, xen-devel@lists.xen.org
Cc: Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Jun Nakajima <jun.nakajima@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>, Jan Beulich <jbeulich@suse.com>, Keir Fraser <keir@xen.org>, Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
List-Id: xen-devel@lists.xenproject.org

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@intel.com>
> ---
>   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