Re: [PATCH 2/4] x86/hvm: Run the RTC periodic timer on a consistent time series.

[Keir Fraser <keir.xen@gmail.com>]

On 28/03/2013 13:22, "Tim Deegan" <tim@xen.org> wrote:

> When the RTC periodic timer gets restarted, align it to the VM's boot
> time, not to whatever time it is now.  Otherwise every read of REG_C
> will restart the current period
> 
> Signed-off-by: Tim Deegan <tim@xen.org>

Looks rather sensible.

Acked-by: Keir Fraser <keir@xen.org>

> ---
>  xen/arch/x86/hvm/rtc.c        |    6 ++++--
>  xen/include/asm-x86/hvm/vpt.h |    3 ++-
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/rtc.c b/xen/arch/x86/hvm/rtc.c
> index 368d3c8..710ae89 100644
> --- a/xen/arch/x86/hvm/rtc.c
> +++ b/xen/arch/x86/hvm/rtc.c
> @@ -91,7 +91,7 @@ void rtc_periodic_interrupt(void *opaque)
>   * RTC_RATE_SELECT settings */
>  static void rtc_timer_update(RTCState *s)
>  {
> -    int period_code, period;
> +    int period_code, period, delta;
>      struct vcpu *v = vrtc_vcpu(s);
>  
>      ASSERT(spin_is_locked(&s->lock));
> @@ -109,7 +109,8 @@ static void rtc_timer_update(RTCState *s)
>          {
>              period = 1 << (period_code - 1); /* period in 32 Khz cycles */
>              period = DIV_ROUND(period * 1000000000ULL, 32768); /* in ns */
> -            create_periodic_time(v, &s->pt, period, period, RTC_IRQ, NULL,
> s);
> +            delta = period - ((NOW() - s->start_time) % period);
> +            create_periodic_time(v, &s->pt, delta, period, RTC_IRQ, NULL, s);
>              break;
>          }
>          /* fall through */
> @@ -741,6 +742,7 @@ void rtc_init(struct domain *d)
>      s->hw.cmos_data[RTC_REG_D] = RTC_VRT;
>  
>      s->current_tm = gmtime(get_localtime(d));
> +    s->start_time = NOW();
>  
>      rtc_copy_date(s);
>  
> diff --git a/xen/include/asm-x86/hvm/vpt.h b/xen/include/asm-x86/hvm/vpt.h
> index c75297b..2e9c7d2 100644
> --- a/xen/include/asm-x86/hvm/vpt.h
> +++ b/xen/include/asm-x86/hvm/vpt.h
> @@ -104,8 +104,9 @@ typedef struct RTCState {
>      struct hvm_hw_rtc hw;
>      /* RTC's idea of the current time */
>      struct tm current_tm;
> +    /* periodic timer */
> +    s_time_t start_time;
>      /* second update */
> -    int64_t next_second_time;
>      struct periodic_time pt;
>      /* update-ended timer */
>      struct timer update_timer;