Hello David, On Friday, August 4, 2006 at 7:50:55 +0100, David Woolley wrote:
> [EMAIL PROTECTED] (Bryan Henderson) wrote: >> Philosophically, the Linux kernel has no business messing with the >> hardware clock. > In engineering terms, it is the most sensible place to do it, because > the kernel is in the position to do this at the most accurate time > without excessive overheads. The method used by Linux kernels to set the RTC, last time I checked, was indeed cheap in terms of processor cycles. But in terms of accuracy, it's also cheap, dead cheap. The kernel sets the RTC in a frame of plus/minus 5 milliseconds (with HZ=100) around the intended time, and without compensation for the exact restart delay of the RTC chip (can add up to 3 ms of error). A roughly calibrated hwclock sets the RTC with a 10 or 20 times better accuracy _at least_. A hundred of microseconds is repeatably achievable. With such figures, my choice is all done. Even if I must admit that the processing overhead is *huge* (but I don't care much). Serge. -- Serge point Bets arobase laposte point net _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
