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SubjectRe: [Xen-devel] [PATCH 2/2] x86/xen: sync the wallclock when the system time changes
>>> On 28.05.13 at 20:22, David Vrabel <david.vrabel@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)?

Jan

> + return 0;
> +
> op.cmd = XENPF_settime;
> - op.u.settime.secs = now->tv_sec;
> - op.u.settime.nsecs = now->tv_nsec;
> + op.u.settime.secs = now.tv_sec;
> + op.u.settime.nsecs = now.tv_nsec;
> op.u.settime.system_time = xen_clocksource_read();
>
> ret = HYPERVISOR_dom0_op(&op);
> if (ret)
> - return ret;
> + return 0;
>
> - /* Set the hardware RTC. */
> - return mach_set_rtc_mmss(now);
> + last = now;
> + next = timespec_add(now, ns_to_timespec(NSEC_PER_SEC / 2));
>
> + return 0;
> }




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