Re: Linux timekeeping plans

Kris Karas (
Fri, 04 Dec 1998 14:02:42 -0500

Stefan Monnier wrote:

> I must say (as an NTP user) that I don't understand: why don't you just
> allow xntpd to use the RTC as a local clock and let xntpd slave ths system
> clock with it ?

The RTC has a precision of 1 second, if memory serves, even though it can
generate interrupts more rapidly. In order for the system to derive more
precision, it must do what hwclock(8) does - watch carefully for the transition
of the seconds digit, and set the kernel's fractional-seconds portion of the
time to zero. This is inherently costly to do. If memory also serves, the RTC
is a slow device - reading it may take a microsecond or more more per byte.

Kristofer Karas                           * (delete X's)
AMA/CCS DoD RF900RR HawkGT !car           *    Senior systems engineer/SysAdmin
"Build a system that even a fool can use, * BI Deaconess Medical Center, Boston
 and only a fool will want to use it."    *  Will design LISP machines for food

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