On Fri, 2007-12-28 at 15:23 -0800, Dean S. Messing wrote:

> Jon, Aaron, I'd like to ask you both to run another test. (Thanks in
> advance.) As root, what does
>
> adjtimex --utc --compare=20 --interval=10 > /tmp/adj_file.txt
>
> give you? (It will take about 3.5 minutes for this to run)
> For the F7 machine on which I'm seeing the weird behaviour,
> I get:
>
>
> [root@medulla ~]# adjtimex --utc --compare=20 --interval=10
> --- current --- -- suggested --
> cmos time system-cmos error_ppm tick freq tick freq
> 1198880050 0.798082
> 1198880059 0.900194 10211.2 10000 10426576
> 1198880069 0.002171 -89802.3 10000 10426576 10899 4022989
> 1198880078 0.104114 10194.3 10000 10426576 9899 4246426
> 1198880087 0.206065 10195.1 10000 10426576 9899 4194864
> 1198880096 0.308030 10196.5 10000 10426576 9899 4102676
> 1198880105 0.409981 10195.1 10000 10426576 9899 4193301
> 1198880114 0.511942 10196.1 10000 10426576 9899 4129239
> 1198880123 0.612893 10095.1 10000 10426576 9900 4192826
> 1198880132 0.714856 10196.3 10000 10426576 9899 4116739
> 1198880141 0.816836 10198.0 10000 10426576 9899 4002676
> 1198880150 0.918770 10193.4 10000 10426576 9899 4305801
> 1198880160 0.020729 -89804.1 10000 10426576 10899 4141739
> 1198880169 0.122682 10195.3 10000 10426576 9899 4180801
> 1198880178 0.224641 10195.9 10000 10426576 9899 4141739
> 1198880187 0.326589 10194.8 10000 10426576 9899 4213614
> 1198880196 0.428548 10195.9 10000 10426576 9899 4141739
> 1198880205 0.530505 10195.7 10000 10426576 9899 4155801
> 1198880214 0.632459 10195.4 10000 10426576 9899 4174551
> 1198880223 0.734426 10196.7 10000 10426576 9899 4088614

> I have no idea what's happening on my F7 system to cause the strange
> behaviour. Does anyone else?
>
>
> Dean
>
Could this be caused by some funny resolution of the system time
delivered by the RTC to the OS? If it delivers time only in seconds, by
uses some strange divider internally, one could see this
behaviour.....
The RTC might still be accurate, but might vary upto one second from the
system clock.

Louis

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On Dec 27, 2007 1:36 AM, Dean S. Messing <deanm@sharplabs.com> wrote:
>
> As root, I just tried doing: `hwclock --show' for the first time on my
> new Dell Precision 490 running F7 and it just hung. Cntl-C broke me out.
>
> I then tried `hwclock --show --debug' and got:
>
> hwclock from util-linux-2.13-pre7
> Using /dev/rtc interface to clock.
> Last drift adjustment done at 1198717263 seconds after 1969
> Last calibration done at 1198717263 seconds after 1969
> Hardware clock is on UTC time
> Assuming hardware clock is kept in UTC time.
> Waiting for clock tick...
> /dev/rtc does not have interrupt functions.
> Waiting in loop for time from /dev/rtc to change
>
> and again the command hung.
>
> I can't seem to set or read the hardware clock (except in the BIOS)
> Anyone know what gives?
>
> uname -a:
>
> Linux medulla 2.6.23.8-34.fc7 #1 SMP Thu Nov 22 20:39:56 EST 2007 x86_64 x86_64 x86_64 GNU/Linux
>
> Dean
>
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Hi Dean,

I am still working on the knowing thing. Did run across an interesting article:

http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=linux&db=man&fname=/usr/share/catman/man8/hwclock.8.html

Have Fun!

Tod

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On Fri, 2007-12-28 at 15:23 -0800, Dean S. Messing wrote:
>
> Jon, Aaron, I'd like to ask you both to run another test. (Thanks in
> advance.) As root, what does
>
> adjtimex --utc --compare=20 --interval=10 > /tmp/adj_file.txt
This is what I get:
--- current --- -- suggested --
cmos time system-cmos error_ppm tick freq tick freq
1198939975 0.245446
1198939985 0.244502 -94.4 10000 0
1198939995 0.243452 -104.9 10000 0 10001 324135
1198940005 0.242234 -121.9 10000 0 10001 1433510
1198940015 0.241303 -93.0 10000 0 10000 6098047
1198940025 0.240238 -106.5 10000 0 10001 428822
1198940035 0.239049 -118.8 10000 0 10001 1235073
1198940045 0.238108 -94.2 10000 0 10000 6171485
1198940055 0.237042 -106.5 10000 0 10001 428822
1198940065 0.235841 -120.2 10000 0 10001 1321010
1198940075 0.234908 -93.3 10000 0 10000 6112110
1198940085 0.233855 -105.4 10000 0 10001 350697
1198940095 0.232636 -121.8 10000 0 10001 1431948
1198940105 0.231711 -92.5 10000 0 10000 6065235
1198940115 0.230483 -122.8 10000 0 10001 1491322
1198940125 0.229438 -104.5 10000 0 10001 292885
1198940135 0.228429 -100.9 10000 0 10001 61635
1198940145 0.227415 -101.3 10000 0 10001 88197
1198940155 0.226205 -121.1 10000 0 10001 1380385
1198940165 0.225268 -93.6 10000 0 10000 6137110

--
================================================== =====================
When I met th'POPE back in '58, I scrubbed him with a MILD SOAP or
DETERGENT for 15 minutes. He seemed to enjoy it ...
================================================== =====================
Aaron Konstam telephone: (210) 656-0355 e-mail: akonstam@sbcglobal.net

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Louis Lagendijk writes:
: On Fri, 2007-12-28 at 15:23 -0800, Dean S. Messing wrote:
: <summary>
: adjtimex --utc --compare=20 --interval=10
: returns values of "system-cmos" that make it look like the RTC
: is "jumping"
:
: Could this be caused by some funny resolution of the system time
: delivered by the RTC to the OS? If it delivers time only in seconds, by
: uses some strange divider internally, one could see this
: behaviour.....
: The RTC might still be accurate, but might vary upto one second from the
: system clock.

Hi Louis.

This is an interesting idea. Do you know of an independent way to
verify it? I guess I'm going to have to find some time (limited!) to
read the kernel docs on /dev/rtc.

If /dev/rtc only delivers time with 1 second granularity that would be
mightly useless, I would think.

One thing that may argue against your idea: each time I invoke

adjtimex --utc --compare=20 --interval=X

X can be _anything_ (I've tried 10, 13, 15, 20, 23, 60),
but the delta between (system-cmos) from line to line
is always almost exactly 0.1 seconds, until the "correction"
occurs.

By the way, I ruled out the possibility of the CMOS clock
running grossly slow. Last evening I turned off
`ntpd', hand set my system clock to freerun using

adjtimex --tick 10001 --freq 3831728

which are the equivalent parameters that ntpd was
using to drive the sytem clock when it was well-tuned.

I also turned off the 11 minute kernel update to the RTC
(with adjtimex -S 64 )

So both clock are free-running.

In 12 hours or so my system clock has drifted from
the "montpelier.ilan.caltech.edu" stratum 1 clock
by only 23 ms (from -0.005 to 0.018) which is less
than 1 ppm. On the other hand


[root@medulla ~]# hwclock --show; date
Sat 29 Dec 2007 12:04:10 PM PST -0.080610 seconds
Sat Dec 29 12:04:09 PST 2007

so my RTC has deviated from system time by no more than
1 second. Indeed it appears be running slightly _fast_
not grossly slow.

Dean

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Tod wrote:
:
: I am still working on the knowing thing. Did run across an interesting article:
:
: http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=linux&db=man&fname=/usr/share/catman/man8/hwclock.8.html

Yep. Try `man hwclock' on your own system. Should be the same thing.
That's the first or second document one shd. read to learn about
system clocks. (The other is the `adjtimex' man page.)

Then, if you want to go deeper, start reading David Mills' documents
on the NTP time protocol. It really is a wonderfully complex and
fascinating technology. People who have experience with PLLs (phase
locked loops) and feedback systems will delight in it.

Dean

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: On Fri, 2007-12-28 at 15:23 -0800, Dean S. Messing wrote:
: >
: > Jon, Aaron, I'd like to ask you both to run another test. (Thanks in
: > advance.) As root, what does
: >
: > adjtimex --utc --compare=20 --interval=10 > /tmp/adj_file.txt
: This is what I get:
<snip>

Thanks Aaron.
What kernel and system (i386 or x86_64) is your data for?
On my FC6 and FC5 machines I have no problems.

Me:

[root@medulla ~]# uname -a
Linux medulla 2.6.23.8-34.fc7 #1 SMP Thu Nov 22 20:39:56 EST 2007 x86_64 x86_64 x86_64 GNU/Linux

Dean

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