linux-kernel - Re: The ext3 way of journalling

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Date:	Mon, 14 Jan 2008 10:57:09 +0100
From:	Bernd Petrovitsch <bernd@...mix.at>
To:	Tuomo Valkonen <tuomov@....fi>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: The ext3 way of journalling

On Mon, 2008-01-14 at 09:48 +0000, Tuomo Valkonen wrote:
> On 2008-01-14, Bernd Petrovitsch <bernd@...mix.at> wrote:
> > Yes, that is a usual bug/problem in common distributions[0] as there is
> > no real guarantee that your clock is not far off.
> 
> It isn't, right after boot. But while the system is on, it sometimes
> starts advancing very fast, 15min a day or so. To my knowledge, the
> time the CMOS clock is not used then, but rather the kernel tracks the

ACK.

> time based on scheduler interrupts, with ntpd occasionally correcting.
> However, ntpd refuses to correct when the time has drifted too much, 
> causing even further drift.

That shouldn't happen.

> > That the reason to activate `ntpdate` unconditionally: It sets the
> > current time to an (somewhat) accurate value and `ntpd` handles the
> > rest.
> 
> Nope, as explained above. ntpdate at boot wouldn't help much, because
> the time is (approximately) correct after boot. It only drifts after it.

Aha. That's also strange. `ntpd` is able to (and always does AFAIK)
modify the speed of the clock (to keep it synchronized) so that the
error is usually much smaller than 1 second - also if you are behind
high-jitter links and/or an a high stratum.
That leads to the question why the clock starts to run like crazy at
some time so that `ntpd` can't cope with it.
Playing with `ntpd` parameters (e.g. increasing ) doesn't help I assume.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services


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