cvs commit: src/contrib/ntp/ntpd ntp_loopfilter.c

[Matthew Dillon]

dillon      2004/01/26 12:58:12 PST

DragonFly src repository

  Modified files:
    contrib/ntp/ntpd     ntp_loopfilter.c 
  Log:
  Fix a serious bug in the NTPD loopfilter.  Basically what happens is that
  when the frequency error is low (e.g. like 15ppm), but an offset correction
  must be made (e.g. like 3 seconds), the rstclock() call loopfilter makes
  in the S_NSET state, after adjusting the system time, will reload a
  clock_offset value PRIOR to the system time adjustment actually having taken
  place, because rstclock() uses offset information prior to the time step, not
  after, and because the kernel may slew the time step over several seconds.
  
  The result is that clock_offset will wind up being very high (e.g. like 3
  seconds) as the loopfilter enters into the S_FREQ state.  This will cause
  the loopfilter to make a wildly incorrect clock_frequency calculation and
  in my tests it can take ntpd and the kernel upwards of one to two DAYS to
  correct for the bad calculation.
  
  The fix is to introduce an offset settling state, S_PFREQ, which resets
  the offset calculations CLOCK_MINSEC seconds after the correction was made
  in order to give the next state, S_FREQ, a good basis for calculating the
  frequency drift.  clock_offset will be far more reasonable when the S_FREQ
  state is entered, a good clock_frequency calculation will be made, and
  ntpd will lock onto the frequency is less then half an hour (instead of
  24+ hours).
  
  Revision  Changes    Path
  1.2       +39 -5     src/contrib/ntp/ntpd/ntp_loopfilter.c


http://www.dragonflybsd.org/cvsweb/src/contrib/ntp/ntpd/ntp_loopfilter.c.diff?r1=1.1&r2=1.2&f=h