Re: [PATCH v2 03/14] x86/time.c: Use correct guest TSC frequency in tsc_set_info()

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 12/06/2015 03:58 PM, Haozhong Zhang wrote:
> When TSC_MODE_PVRDTSCP is used for a HVM container and TSC scaling is
> available, use the non-zero value of argument gtsc_khz of tsc_set_info()
> as the guest TSC frequency rather than using the host TSC
> frequency. Otherwise, TSC scaling will not be able get the correct ratio
> between the host and guest TSC frequencies.
>
> Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> ---
>   xen/arch/x86/time.c | 11 +++++++++--
>   1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index b5223cf..1091e69 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -1803,6 +1803,8 @@ void tsc_set_info(struct domain *d,
>                     uint32_t tsc_mode, uint64_t elapsed_nsec,
>                     uint32_t gtsc_khz, uint32_t incarnation)
>   {
> +    bool_t enable_tsc_scaling;
> +
>       if ( is_idle_domain(d) || is_hardware_domain(d) )
>       {
>           d->arch.vtsc = 0;
> @@ -1864,7 +1866,9 @@ void tsc_set_info(struct domain *d,
>       case TSC_MODE_PVRDTSCP:
>           d->arch.vtsc = !boot_cpu_has(X86_FEATURE_RDTSCP) ||
>                          !host_tsc_is_safe();
> -        d->arch.tsc_khz = cpu_khz;
> +        enable_tsc_scaling = has_hvm_container_domain(d) &&
> +                             cpu_has_tsc_ratio && d->arch.vtsc;
> +        d->arch.tsc_khz = (enable_tsc_scaling && gtsc_khz) ? gtsc_khz : cpu_khz;
>           set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
>           d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
>           if ( d->arch.vtsc )
> @@ -1872,7 +1876,10 @@ void tsc_set_info(struct domain *d,
>           else {
>               /* when using native TSC, offset is nsec relative to power-on
>                * of physical machine */
> -            d->arch.vtsc_offset = scale_delta(rdtsc(), &d->arch.vtsc_to_ns) -
> +            struct time_scale *scale = enable_tsc_scaling ?

Do we need this test here? Per previous chunk, enable_tsc_scaling will 
be zero since d->arch.vtsc is false.

Actually, if you are trying to use (or, rather, account for) TSC 
scaling, shouldn't it be !arch.vtsc there?


-boris

> +                                       &this_cpu(cpu_time).tsc_scale :
> +                                       &d->arch.vtsc_to_ns;
> +            d->arch.vtsc_offset = scale_delta(rdtsc(), scale) -
>                                     elapsed_nsec;
>           }
>           break;