Serge, The NTP clock discipline doesn;t work like that. The ntpdate and imitator compute an offset correction, hand off the adjtime() and go home. The NTP clock discipine algorithm incorporates a feedback loop which includes a proportional control with time constant of several teens of minutes. See the arthictecture briefing at the NTP project page.
Dave Serge Bets wrote: > Hello David, > > On Saturday, May 5, 2007 at 15:03:26 +0100, David Woolley wrote: > > >>Steve Kostecke <[EMAIL PROTECTED]> wrote: >> >>>If your clock is less than 128ms off ntpd slews it. The slew will take >>>the same amount of time regardless of how ntpd is running (e.g. as a >>>daemon or via a cron-job w/ -gq). >> >>My impression is that -gq will be faster. ntpdate is certainly faster. > > > I agree, and experimented with a 30 ms offset. The box has the good > frequency both in kernel (ntptime -f) and in driftfile. The ntp.conf > declares one server with iburst, and the driftfile. Slewing 30 ms at > 500 PPM should take exactly 60 seconds, right? I monitored with repeated > ntpdate -q until zero offset: > > - ntpdate took 60 seconds. > > - ntpd -gq took 67 seconds. I guess 7 seconds to determine the offset, > and 60 to slew it (execution time is 7 seconds). > > - ntpd -g took much much longer... It took 7 minutes to cross the zero > offset for the first time. But the frequency was then wildly off (about > 12 PPM over normal). Offset overshoot by about 8 ms in one way then the > other. Finally offset and frequency both stabilized. After 4 hours. > > 4 hours to amortize a 30 ms offset at startup... that's a high cost for > stopping machines during the night. > > > >>The 0.5ms/s slew rates are relative to the static error in the machine >>clock, so they can reduce to almost 0 in one direction and almost >>1ms/s in the other, in a system with a clock at the margins of >>usability. > > > Are you sure? I have here a machine whose natural driftfile is -100 PPM. > It still seems to slew 500 PPM in both directions, not -400 +600. > > > Serge. _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
