QUESTION: What results in best timekeeping by the RTC, constant
updates or logging the offset?
ANSWER:
The Linux kernel code for the 11 minute update in
arch/i386/kernel/time.c has an RTC setting error of +-0.005 s. The
adjtimex source suggests an RTC reading error of +-0.000025 s.
Accurate RTC timekeeping also requires an accurate value of average
drift rate for typical use. Measuring this requires timing over a long
unset period such as one month.
Logging the offset is more accurate per reading and allows
more accurate measurement of drift than 11 minute updates.
END ANSWER.
RTC accuracy supports optionalizing the 11 minute update.
Other reasons to optionalize the 11 minute update which various people
suggest:
1. The kernel should not dictate OS policy;
2. Simplifies programming with /dev/rtc;
3. Improves performance of /dev/rtc;
4. Slightly reduced kernel size;
5. Slightly faster timer_interrupt;
6. Easier to use utilities like hwclock.
I agree with you, Pavel. Commenting out the 11 minute update
code is a better solution. :)
> Pavel
> --
> Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
> details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.
>
-- Regards, Ian Maclaine-cross (iml@debian.org) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/