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Date:      Wed, 22 Mar 2006 08:22:35 -0500
From:      Bill Moran <wmoran@collaborativefusion.com>
To:        alfred.morgan@experclick.com
Cc:        freebsd-questions@freebsd.org
Subject:   Re: clock drifts after upgrade from 5.x to 6.x
Message-ID:  <20060322082235.c5d62721.wmoran@collaborativefusion.com>
In-Reply-To: <7c61221qt0meet1dudmids5vgcisejjjth@4ax.com>
References:  <44204E79.4090408@experclick.com> <7c61221qt0meet1dudmids5vgcisejjjth@4ax.com>

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On Wed, 22 Mar 2006 00:46:57 +0000
John Murphy <sub02@freeode.co.uk> wrote:

> Alfred Morgan <alfred.morgan@experclick.com> wrote:
> 
> >
> >   I have upgraded 4 different machines from various FreeBSD versions of
> >   5 to various versions of 6 and 3 of the machines has a problem where
> >   the clock will drift very quickly slowing about 2 seconds per minute.
> 
>    Interesting.  Were all the upgrades from versions less than 5.3
>    I wonder? Reason I ask is that many people (including me) seem to
>    have started having problems with ntp around that time.  There was
>    a thread in the stable mailing list about it here:
>    http://docs.freebsd.org/cgi/mid.cgi?20050401104508.GJ71384

Most machines these days have a number of clocks available.  ACPI
is likely choosing a less accurate clock than you would like.
Apparently, with ACPI disabled, the default clock is pretty
accurate.  The worst examples of this are when you get calcru()
errors because the clock actually appears to tick backwards
sometimes.

You can manually tell FreeBSD which clock to use via sysctl.  I
don't remember the magic incanation, but a few google searches
should set you on the right path.  Search for timecounter and calcru
in addition to other terms relevent to your issue.

-- 
Bill Moran
Collaborative Fusion Inc.



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