On 2012-02-02, David Lord <[email protected]> wrote: > unruh wrote: >> On 2012-02-02, David J Taylor <[email protected]> wrote: >>>> On NetBSD-5 with ntpd 4.2.6p5 the default is 64s. >>> I wonder what expertise they have to select polling for reference clocks? >>> BTW: Paul has FreeBSD. >> >> The reason for longer polling is a) network load, and b) rate >> optimality. >> If you are running ntp in order that your computer clock be ticking at >> exactly 1s/s, then longer polls are better (longer lever arm) if your >> computer clock does not change rate (eg due to internal temperature >> changes due to use of the computer) If, you want least deviationo of the >> clock from UTC shorter polls are better. Since the primary ntp noise >> source, variable network delays, is not there, and since the primary >> noise source is interrupt servicing delays, shorter is probably better. >> >>>> I've just added the "minpoll 4 maxpoll 4" back to my ntp.conf >>>> as it could reduce the 30 usec offset blips I get when logs are >>>> rotated. >> >> Not sure what would cause 30us blips. Are interrupts really being >> switched off by something for those lengths of time? > > It's the load from log rotation and cron jobs running at > that time of night.
The load should not matter. The interrupt sevice routines take precidence. Now it might be that the interrupt routines require paging in, but I thought that IRQ servicing was kept in memory as much as possible. IRQs have to be fast. And 30us is a HUGE time (over 10,000 cpu instructions) > > > David Lord _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
