[ntp:questions] Linux 11-minute mode (RTC update)
Serge Bets
serge.bets at NOSPAM.laposte.invalid
Fri Apr 4 10:45:20 UTC 2008
Hello,
On Thursday, April 3, 2008 at 16:25:17 +0200, Noob wrote:
> STA_UNSYNC (0x0040, clock unsynchronized) is 0. [...] Thus the kernel
> should write the system time to the RTC every 11 minutes; but it does
> not.
Fine! Don't touch anything, happy man, or it might well "tomber en
marche". Real men don't want the eleven-minutes mode. It is not only
extremely inaccurate by itself, but it also steps on the toes of those
tools that are able to manage the RTC properly.
I previously posted some figures, comparing the accuracy of writing the
RTC (not counting drift). Mean offset and dispersion:
- eleven-minutes mode: -2150 µs +-5000
- hwclock util-linux-ng 2.13.1: -2500 µs +-170
- hwclock 2.32 from BJH: 0 µs +-10
Furthermore both hwclocks are able to evaluate and compensate the drift
of the RTC. The eleven-minutes mode cannot do that, and instead it can
perturbate hwclock's calculations.
Serge.
--
Serge point Bets arobase laposte point net
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