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The Thursday 2007-12-13 at 21:38 -0000, Roger Hayter wrote:
I don't think it is directly related to your problem, but as an example where
the Linux system clock is not good enough for ntp I have a machine runing
SuSE 9.3 which gains 0.28 seconds every hour on system time (nothing to do
with CMOS clock!!). "ntpd" just refuses to synchronise this machine, and from
the docs I gather this is expected behaviour if system time is too far out.
I assumed this might be a hardware problem, perhaps an unstable or incorrect
CPU clock signal.
I don't believe in hardware problems. I think it is bad programming
somewhere. Or the wrong choice of clock type by the kernel.
Do 'ls /sys/devices/system/clocksource/'. There should be a directory
there (if there are more I don't know what they are) named "clocksource0".
Look in there. There should be two files there: available_clocksource and
current_clocksource. Do a 'cat' on both:
nimrodel:~ # cat /sys/devices/system/clocksource/clocksource0/*
acpi_pm pit jiffies tsc
tsc
nimrodel:~ #
One is the types of system clocks in your system the kernel knows about,
and the other is the one it is using.
I know very little about them.
The acpi_pm is related to some acpi hardware, and in mine is very wrong.
The pit one I have no idea.
The tsc one seems correct in mine, but may be problematic: I'm watching
it closely. I don't know what type of clock it is really.
The jiffies type is the classic one, I think. Try that one on your pc, it
should work - this command changes the running clock:
echo jiffies >
/sys/devices/system/clocksource/clocksource0/current_clocksource
If I'm correct, this one is simply a counter updated by an interrupt from
an 8250? oscillator. The frequency of this oscillator can be corrected:
that's what ntp does, I think.
An educated guess on my part, of course.
HTH
- --
Cheers,
Carlos E. R.
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