On 29/05/13 08:39, Jan Beulich wrote:
>>>> On 28.05.13 at 20:22, David Vrabel <david.vra...@citrix.com> wrote:
>> +static int xen_pvclock_gtod_notify(struct notifier_block *nb, unsigned long
>> unused,
>> + void *priv)
>> +{
>> + static struct timespec last, next;
>> + struct timespec now;
>> + struct timekeeper *tk = priv;
>> + struct xen_platform_op op;
>> + int ret;
>> +
>> + /*
>> + * Set the Xen wallclock from Linux system time.
>> + *
>> + * dom0 hasn't historically maintained a very accurate
>> + * wallclock so guests don't expect it. We can therefore
>> + * reduce the number of expensive hypercalls by only updating
>> + * the wallclock every 0.5 s.
>> + */
>> +
>> + now.tv_sec = tk->xtime_sec;
>> + now.tv_nsec = tk->xtime_nsec >> tk->shift;
>> +
>> + if (timespec_compare(&now, &last) > 0
>> + && timespec_compare(&now, &next) < 0)
>
> Is this really working the first time through (when both last and
> next are still all zeros)?
Yes. The first time through we want to set the wallclock and this test
is always false when last == next.
David
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