[ntp:questions] Linux 11-minute mode (RTC update)

Unruh unruh-spam at physics.ubc.ca
Sun Apr 6 19:36:40 UTC 2008

Serge Bets <serge.bets at NOSPAM.laposte.invalid> writes:

> On Saturday, April 5, 2008 at 18:27:37 +0000, Unruh wrote:

>> Serge Bets <serge.bets at NOSPAM.laposte.invalid> writes:
>>> Depending on the mode of operation, hwclock consumes either much
>>> more, or enormously more cycles.
>> By enourmously more you mean 100 rather than 10 cycles?

>I don't have the exact timings at hand, but it's yet more. The
>eleven-minutes write takes some tens of microseconds; normal hwclock
>some tens of milliseconds; hwclock --nointerrupt some plain seconds.

To write the rtc properly takes at least a second. The rtc ONLY reports
once a second and is set to the time you supply when you write it. Thus you
have to make sure that you write at exactly the right time or the rtc will
be out by up to a second. 

>> The rate of the rtc is important when the machine is off (cold)

>Again, what you say is true in the general case. Not at all, or less, in
>the OP case (24/7 servers rarely and shortly off).

In the case the machine comes up again in a few seconds, the rate
correction is irrelevant anyway. And if the system reads the clock badly it
will be out by about a second anyway. 

>> one of my machines has an rtc clock that varies from 0PPM to 100PPM
>> with a few degree temp change-- I think the rtc may be dying.

>Aouch! Indeed totally out of bounds.

I agree. Not sure what is happening. 

>Serge point Bets arobase laposte point net

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