Re: [Xen-devel] [PATCH v3 02/13] x86/time.c: Use correct guest TSC frequency in tsc_get_info()

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/30/2015 10:03 PM, Haozhong Zhang wrote:
> When the TSC mode of a HVM container is TSC_MODE_DEFAULT or
> TSC_MODE_PVRDTSCP and no TSC emulation is used, the existing
> tsc_get_info() uses the host TSC frequency (cpu_khz) as the guest TSC
> frequency. However, tsc_set_info() may set the guest TSC frequency to a
> value different than the host. In order to keep consistent to
> tsc_set_info(), this patch makes tsc_get_info() use the value set by
> tsc_set_info() as the guest TSC frequency.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> ---
> Changes in v3:
>   (addressing Boris Ostrovsky's comments)
>   * Use this_cpu(cpu_time).tsc_scale for both scaling and non-scaling cases.
>
>   xen/arch/x86/time.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index 0059b6a..d83f068 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -1749,6 +1749,9 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
>                     uint64_t *elapsed_nsec, uint32_t *gtsc_khz,
>                     uint32_t *incarnation)
>   {
> +    bool_t enable_tsc_scaling = has_hvm_container_domain(d) &&
> +                                cpu_has_tsc_ratio;
> +
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

although I still think that having !d->arch.vtsc would be better, even 
if not strictly required.


>       *incarnation = d->arch.incarnation;
>       *tsc_mode = d->arch.tsc_mode;
>   
> @@ -1769,7 +1772,7 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
>           }
>           tsc = rdtsc();
>           *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns);
> -        *gtsc_khz = cpu_khz;
> +        *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz : cpu_khz;
>           break;
>       case TSC_MODE_PVRDTSCP:
>           if ( d->arch.vtsc )
> @@ -1780,9 +1783,9 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
>           else
>           {
>               tsc = rdtsc();
> -            *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns) -
> +            *elapsed_nsec = scale_delta(tsc, &this_cpu(cpu_time).tsc_scale) -
>                               d->arch.vtsc_offset;
> -            *gtsc_khz = 0; /* ignored by tsc_set_info */
> +            *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz : 0;
>           }
>           break;
>       }

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