clock problem

[Ian Smith]

On Fri, 11 May 2007, Tom Evans wrote:
 > On Fri, 2007-05-11 at 08:53 -0600, M. Warner Losh wrote:
 > > In message: <20070511110759.L700 at thinkpad.dieringer.dyndns.org>
 > >             Martin Dieringer <martin.dieringer at 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

Yes, but Martin already showed it was using the i8254, not TSC; would
you expect the same effect using powerd with the i8254 clock?  It seems
so, unless it's some problem with est and/or p4tcc under APM (canoworms)

Runnning APM, at least on my ol' Compaq 1500c 5.5-S running APM - really
too ancient to expect ACPI to work properly - on verbose boot states: 

Calibrating clock(s) ... i8254 clock: 1193216 Hz
CLK_USE_I8254_CALIBRATION not specified - using default frequency
Timecounter "i8254" frequency 1193182 Hz quality 0
Calibrating TSC clock ... TSC clock: 300011839 Hz
[..]
TSC timecounter disabled: APM enabled.                     <<<<<<<<<<<<
Timecounter "TSC" frequency 300011839 Hz quality -1000

ie:
kern.timecounter.hardware: i8254
kern.timecounter.choice: TSC(-1000) i8254(0) dummy(-1000000)

 > Surely that would imply that it is a software misconfiguration issue. If
 > the TSC is unreliable under fairly standard duties, and there exists an
 > alternate source that is reliable, surely that indicates the
 > manufacturer has identified a problem, and solved it with alternate
 > hardware.
 > 
 > The failure then to use the correct hardware is a software
 > misconfiguration.

If one considers disabling ACPI and enabling APM misconfiguration ..
which in Martin's case it turned out to be, since his ACPI works, but

 est0: <Enhanced SpeedStep Frequency Control> on cpu0
 p4tcc0: <CPU Frequency Thermal Control> on cpu0
 apm0: <APM BIOS> on motherboard
 apm0: found APM BIOS v1.2, connected at v1.2

together with powerd appeared to heavily retard time on both laptops,
beyond ntpd's ability to cope.

Cheers, Ian