Re: [Xen-devel] [PATCH 2/2] x86/time: report correct frequency of Xen PV clocksource

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Feb 04, 2020 at 03:40:25PM +0000, Igor Druzhinin wrote:
> The value of the counter represents the number of nanoseconds
> since host boot. That means the correct frequency is always 1GHz.
> 
> This inconsistency caused time to go slower in PV shim on most
> platforms.
> 
> Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

With one nit below.

> ---
>  xen/arch/x86/time.c | 17 +----------------
>  1 file changed, 1 insertion(+), 16 deletions(-)
> 
> diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> index 7e7a62e..95840c4 100644
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -567,27 +567,12 @@ static struct platform_timesource __initdata plt_tsc =
>   */
>  static uint64_t xen_timer_last;
>  
> -static uint64_t xen_timer_cpu_frequency(void)
> -{
> -    struct vcpu_time_info *info = &this_cpu(vcpu_info)->time;
> -    uint64_t freq;
> -
> -    freq = 1000000000ULL << 32;
> -    do_div(freq, info->tsc_to_system_mul);
> -    if ( info->tsc_shift < 0 )
> -        freq <<= -info->tsc_shift;
> -    else
> -        freq >>= info->tsc_shift;
> -
> -    return freq;
> -}
> -
>  static int64_t __init init_xen_timer(struct platform_timesource *pts)
>  {
>      if ( !xen_guest )
>          return 0;
>  
> -    pts->frequency = xen_timer_cpu_frequency();
> +    pts->frequency = 1000000000ULL;

You can init this field below at declaration, since it's a static
value.

Thanks, Roger.

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