【chrony】smoothtime パラメータについて

  Time smoothing determines an offset that needs to be applied to the cooked
  time to make it smooth for external observers.  Observed offset and frequency
  change slowly and there are no discontinuities.  This can be used on an NTP
  server to make it easier for the clients to track the time and keep their
  clocks close together even when large offset or frequency corrections are
  applied to the server's clock (e.g. after being offline for longer time).

  Accumulated offset and frequency are smoothed out in three stages.  In the
  first stage, the frequency is changed at a constant rate (wander) up to a
  maximum, in the second stage the frequency stays at the maximum for as long
  as needed and in the third stage the frequency is brought back to zero.

              |
    max_freq  +-------/--------\-------------
              |      /|        |\
        freq  |     / |        | \
              |    /  |        |  \
              |   /   |        |   \
           0  +--/----+--------+----\--------
              | /     |        |    |    time
              |/      |        |    |

        stage     1       2      3

  Integral of this function is the smoothed out offset.  It's a continuous
  piecewise polynomial with two quadratic parts and one linear.