From: Bill Fink <billfink@mindspring.com>
To: LinuxPPC Developers <linuxppc-dev@lists.linuxppc.org>
Cc: Bill Fink <billfink@mindspring.com>
Subject: Re: Time precision, adjtime(x) vs. gettimeofday
Date: Fri, 10 Oct 2003 01:12:54 -0400 [thread overview]
Message-ID: <20031010011254.078c84a8.billfink@mindspring.com> (raw)
On Wed, 08 Oct 2003, Benjamin Herrenschmidt wrote:
> > I repeat the question: what are the values of drift on the machines
> > that encounter the problem ? Is this drift stable or unstable?
>
> So far, there is no problem. The problem that was happening
> was a via_calibrate_decr() bug with HZ != 100, but when
> investigating, I figured out that we had a potential problem
> there, that's all and that's why I want people like you who
> know those problems well to state if it's worth bothering ;)
>
> > > On all cases, those will drift some way from what the NTP server
> > > will give, either a lot or not, it will. So we may end up adjusting
> > > our kernel rate and thus opening a window for the problem.
> >
> > The worst variations of drift I've seen are a few ppm for a given
> > machine, barring the occasional boot-time calibration problems that I
> > have encountered.
>
> OK.
This discussion prompted me to finally ask about another clock related
problem I see on the 867 MHz G4 systems at work. The clocks on these
systems continuously run 0.2% slow (about 3 minutes per day). Apparently
this is more than ntp can adjust for (using scaling), as I get many of
these error messages in the log:
Oct 10 00:11:29 clifford ntpd[425]: time reset 2.641342 s
Oct 10 00:11:29 clifford ntpd[425]: synchronisation lost
Oct 10 00:32:07 clifford ntpd[425]: time reset 2.671741 s
Oct 10 00:32:07 clifford ntpd[425]: synchronisation lost
Oct 10 00:52:46 clifford ntpd[425]: time reset 2.671729 s
Oct 10 00:52:46 clifford ntpd[425]: synchronisation lost
This causes problems if I take these systems off the network for a few
hours, if I forget to reset them to the correct time when I reconnect
them, since we use Kerberos for security, and the time difference between
the system and the Kerberos KDC will prevent remote logins.
These systems are using a 2.4.20-ben1 kernel.
-Bill
** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/
next reply other threads:[~2003-10-10 5:12 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-10 5:12 Bill Fink [this message]
2003-10-10 7:33 ` Time precision, adjtime(x) vs. gettimeofday Gabriel Paubert
2003-10-10 16:39 ` Bill Fink
2003-10-10 7:53 ` Ethan Benson
-- strict thread matches above, loose matches on Subject: below --
2003-10-11 4:45 Bill Fink
2003-10-11 5:27 ` Ethan Benson
2003-10-11 14:58 ` Benjamin Herrenschmidt
2003-10-14 7:07 ` Gabriel Paubert
2003-10-14 11:16 ` Benjamin Herrenschmidt
2003-10-08 13:32 Benjamin Herrenschmidt
2003-10-08 15:48 ` Gabriel Paubert
2003-10-08 16:22 ` Benjamin Herrenschmidt
2003-10-08 17:50 ` Gabriel Paubert
2003-10-08 18:22 ` Benjamin Herrenschmidt
2003-10-08 22:17 ` Pavel Machek
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