Re: [Xen-devel] [PATCH 5/5] x86/xen: sync the CMOS RTC as well as the Xen wallclock

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Thu, 27 Jun 2013, David Vrabel wrote:

> From: David Vrabel <david.vrabel@xxxxxxxxxx>
> 
> Adjustments to Xen's persistent clock via update_persistent_clock()
> don't actually persist, as the Xen wallclock is a software only clock
> and modifications to it do not modify the underlying CMOS RTC.
> 
> The x86_platform.set_wallclock hook can be used to keep the hardware
> RTC synchronized (as on bare metal).  Because the Xen wallclock is now
> kept synchronized by pvclock_gtod notifier, xen_set_wallclock() need
> not do this and dom0 can simply use the native implementation.

I can understand that part, but ...
 
>  static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long 
> was_set,
>                                  void *priv)
>  {
> +     static struct timespec next;
>       struct timespec now;
>       struct xen_platform_op op;
>  
> -     if (!was_set)
> -             return NOTIFY_OK;
> -
>       now = __current_kernel_time();
>  
> +     if (!was_set && timespec_compare(&now, &next) < 0)
> +             return NOTIFY_OK;
> +
>       op.cmd = XENPF_settime;
>       op.u.settime.secs = now.tv_sec;
>       op.u.settime.nsecs = now.tv_nsec;
>       op.u.settime.system_time = xen_clocksource_read();
>  
>       (void)HYPERVISOR_dom0_op(&op);
> +
> +     /*
> +      * Don't update the wallclock for another 11 minutes. This is
> +      * the same period as the sync_cmos_clock() work.
> +      */
> +     next = now;
> +     next.tv_sec += 11*60;
> +

How is this related to the changelog? /me is confused .....


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