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

Unruh unruh-spam at physics.ubc.ca
Thu Jul 24 18:02:01 UTC 2008


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

> On Thursday, July 24, 2008 at 1:48:40 +0000, Bill Unruh wrote:

>> Apparently the HPET disables the rtc interrupts and takes them over.

>Those HPET emulated RTC interrupts indeed seem to be nothing else than
>unusable rubbish, by design. They introduce an unacceptable level of
>error in the measures. Error 4 orders of magnitude greater than what's
>reasonably expectable from proper RTC interrupts.

The problem is a balance between uacceptable number of interrupts vs
accuracy. Having100KHz interrupt rate just to impliment UIE would be
unacceptable. 



>> No amount of care in the hwclock program can get around this kind of
>> nonesense.

>Exactly. Disabling HPET seems the only solution to have proper RTC
>interrupts. Alternatively tell hwclock to *not* use interrupts, via
>either the --directisa or --nointerrupt options. This is less elegant,
>and costs many processor cycles. But accuracy should be good.


>Serge.
>-- 
>Serge point Bets arobase laposte point net




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