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Date: Fri, 11 May 2007 08:53:25 -0600 (MDT)
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To: martin.dieringer@gmx.de
From: "M. Warner Losh" <imp@bsdimp.com>
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	Fri, 11 May 2007 08:53:21 -0600 (MDT)
Cc: freebsd-stable@FreeBSD.ORG
Subject: Re: clock problem
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In message: <20070511110759.L700@thinkpad.dieringer.dyndns.org>
            Martin Dieringer <martin.dieringer@gmx.de> writes:
: This is NOT a hardware problem. 1. I have this on 2 machines, 2. the
: problem is solved by switching to ACPI instead of APM

It is a hardware problem.  APM + powerd changes the frequency of the
TSC.  If the TSC is used as the time source, then you'll get bad
timekeeping.  ACPI uses its own frequency source that is much more
stable and independent of the TSC, so switching to it fixes the
problem because you are switching the hardware from using a really bad
frequency source with ugly steps to using a good frequency source w/o
steps.

Warner