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SubjectRe: [PATCH] ntp: Make periodic RTC update more reliable
On 08/01/2013 10:31 AM, Miroslav Lichvar wrote:
> The current code requires that the scheduled update of the RTC happens
> in the closest tick to the half of the second. This seems to be
> difficult to achieve reliably. The scheduled work may be missing the
> target time by a tick or two and be constantly rescheduled every second.
>
> Relax the limit to 10 ticks. As a typical RTC drifts in the 11-minute
> update interval by several milliseconds, this shouldn't affect the
> overall accuracy of the RTC much.
>
> Signed-off-by: Miroslav Lichvar <mlichvar@redhat.com>
> ---
> kernel/time/ntp.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
> index 8f5b3b9..ab1fa7c 100644
> --- a/kernel/time/ntp.c
> +++ b/kernel/time/ntp.c
> @@ -475,6 +475,7 @@ static void sync_cmos_clock(struct work_struct *work)
> * called as close as possible to 500 ms before the new second starts.
> * This code is run on a timer. If the clock is set, that timer
> * may not expire at the correct time. Thus, we adjust...
> + * We want the clock to be within a couple of ticks from the target.
> */
> if (!ntp_synced()) {
> /*
> @@ -485,7 +486,7 @@ static void sync_cmos_clock(struct work_struct *work)
> }
>
> getnstimeofday(&now);
> - if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec / 2) {
> + if (abs(now.tv_nsec - (NSEC_PER_SEC / 2)) <= tick_nsec * 5) {
> struct timespec adjust = now;
>
> fail = -ENODEV;

Applied to my 3.12 branch.

thanks
-john


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