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Message-ID: <e2e108260804162317s5162a6cds151bba6abf988921@mail.gmail.com>
Date: Thu, 17 Apr 2008 08:17:31 +0200
From: "Bart Van Assche" <bart.vanassche@gmail.com>
To: "Marc Perkel" <mperkel@yahoo.com>
Subject: Re: AMD Quad Core clock problem?
Cc: "Chris Snook" <csnook@redhat.com>, linux-kernel@vger.kernel.org
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On Wed, Apr 16, 2008 at 11:44 PM, Marc Perkel <mperkel@yahoo.com> wrote:
>  --- Bart Van Assche <bart.vanassche@gmail.com> wrote:
>  > It's better to correct the clock frequency once with
>  > the tickadj or adjtimex, so you don't have to add
>  > ntpdate to cron and you can still run ntpd.
>  >
>  > Bart.
>
>  ok - thanks. How do I do that?

You can do that as follows:
* First of all, make sure that adjtimex is installed. Some distro's
include this command in util-linux.
* Query the current tick value via adjtimex -p | grep tick. E.g. with
HZ = 100, tick == 10000.
* Multiply the tick value with the relative clock error: when e.g. 3s
are lost every hour, the correct tick value is 10000 * (1 + 3/3600) =
10008.
* Pass this new tick value to the kernel via adjtimex -t 10008.
* Stop and restart ntpd such that it forgets any previous frequency estimates.
* Keep an eye on the output of adjtimex -p|grep frequency to see
whether the frequency estimate converges (should be stable within 10
ppm after an hour. See also man adjtimex for the units of this value).

Bart.