| Re: [chrony-users] gpsd, pps and chrony |
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On Thu, 7 Apr 2011, Ed W wrote:
On 06/04/2011 21:58, Miroslav Lichvar wrote:
On Wed, Apr 06, 2011 at 07:18:24PM +0100, Ed W wrote:
- I see a clear connection between my cpu Mhz as reported in say
/proc/cpuinfo (unknown if this source is reliable when processor
powersave in use?) and the stable chrony tracking parameters
At least here, MHz in /proc/cpuinfo is affected by powersaving and it
is a nicely rounded value, not what kernel prints in dmesg.
I'm quite surprised that others don't see this gross variation that I
do? For me at least I get no value at all from chrony's saved tracking
params because chrony is tracking an average offset of around 130ppm,
but the bootup variation is some 100+ ppm around that offset? Do others
get less variation with each boot?
I just made a test with a 2.6.38-rc0 kernel and I have good
news for you :). I noticed this in dmesg:
Detected 3192.489 MHz processor.
Refined TSC clocksource calibration: 3191.999 MHz
Hmm, will give it a try shortly.
It seems to be this commit, merged just few months ago.
http://git.kernel.org/?p=linux/kernel/git/x86/linux-2.6-tip.git;a=commitdiff;h=08ec0c58fb8a05d3191d5cb6f5d6f81adb419798
Ahh, interesting - sadly the Alix has no PM or HPET timers so I think
this is unlikely to help *my* specific case, but it's very good news in
general!
In order to get a good estimate of the time, the machine must have an internal
timer of some sort. The usual technique seems to use a sound source, and a
timing loop. Of course sitting in that timing loop for a second stops the
whole bootup for a second. The point of that recalibration seems that it can
be done in the background. Do you have any kind of independent time (eg an
RTC) on your system?
Ed W
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