Re: [Xen-devel] [PATCH v4 3/5] x86/time: refactor read_platform_stime()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.09.16 at 19:37, <joao.m.martins@xxxxxxxxxx> wrote:
> To allow the caller to fetch the last read from the clocksource which
> was used to calculate system_time. This is a prerequisite for a
> subsequent patch that will use this last read.
> 
> Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with one further minor request:

> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -581,18 +581,22 @@ static void plt_overflow(void *unused)
>      set_timer(&plt_overflow_timer, NOW() + plt_overflow_period);
>  }
>  
> -static s_time_t read_platform_stime(void)
> +static s_time_t read_platform_stime(u64 *stamp)
>  {
> -    u64 count;
> +    u64 plt_counter, count;
>      s_time_t stime;
>  
>      ASSERT(!local_irq_is_enabled());
>  
>      spin_lock(&platform_timer_lock);
> -    count = plt_stamp64 + ((plt_src.read_counter() - plt_stamp) & plt_mask);
> +    plt_counter = plt_src.read_counter();
> +    count = plt_stamp64 + ((plt_counter - plt_stamp) & plt_mask);
>      stime = __read_platform_stime(count);
>      spin_unlock(&platform_timer_lock);
>  
> +    if ( stamp )
> +        *stamp = plt_counter;

Considering that all current callers pass in NULL and you mean to
add only one (iirc) which doesn't, please add unlikely() here.

Jan


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