Re: very odd hardware clock behavior

Jeff DeFouw (defouwj@purdue.edu)
Fri, 10 Dec 1999 16:01:13 -0500 (EST)


On Fri, 10 Dec 1999, Guest section DW wrote:

> Yes - you want to kill this 11 minute mode in the kernel.

What is "11 minute mode" anyway? I did happen to catch that thread on a
web archive (where I read linux-kernel regularly) but didn't see any
explanation. Or maybe I just don't want to know...

> Concerning the messages:
>
> Suppose set_rtc_mmss() is called just before the hour.
> Say real_minutes=59 and cmos_minutes=0.
> What happens?
> A message in syslog.

How odd. In any case, its obviously not staying in synch even when it
succeeds as it does this every hour.

> Concerning a hwclock hang:
> Did you try "hwclock --directisa"?
> For many people that works better than accessing the hardware clock
> via /dev/rtc and the kernel.

Yes. The only difference is my system gets really sluggish as it hammers
out the I/O. Still just sits there.

> Concerning the "last I was able to run hwclock it was about 40 minutes off":
>
> There is the silly code
>
> So when things go a bit wrong, the kernel will add 30 minutes to the
> error in the hardware clock.

Somehow it managed to *subtract* almost three *years* from my hardware
clock. If it's supposed to add it's doing something REALLY wrong. :)

> How could things go a bit wrong? Hmm. There is also /etc/adjtime that
> tries to follow the drift of the clock. Bad things will happen if
> you set up hwclock to use /etc/adjtime and simultaneously have this
> 11 minute mode. Wild fluctuations may be the result.

Well I haven't set any of this up myself. I have ntpd keeping in sync
with a nearby router, and just the hwclock system<->hardware setup before
booting everything and after shutting down everything. This has never
been a problem until Nov 17 when I began a constant CPU load of 2.00+
running the distnet CSC contest. There were no hwclock hangs or any
set_rtc_mmss messages before then.

--
Jeff DeFouw <defouwj@purdue.edu>

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