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Diffstat (limited to 'smooth.c')
| -rw-r--r-- | smooth.c | 364 |
1 files changed, 364 insertions, 0 deletions
diff --git a/smooth.c b/smooth.c new file mode 100644 index 0000000..4125ea0 --- /dev/null +++ b/smooth.c @@ -0,0 +1,364 @@ +/* + chronyd/chronyc - Programs for keeping computer clocks accurate. + + ********************************************************************** + * Copyright (C) Miroslav Lichvar 2015 + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of version 2 of the GNU General Public License as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + * + ********************************************************************** + + ======================================================================= + + Routines implementing time smoothing. + + */ + +#include "config.h" + +#include "sysincl.h" + +#include "conf.h" +#include "local.h" +#include "logging.h" +#include "reference.h" +#include "smooth.h" +#include "util.h" + +/* + 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. +*/ + +struct stage { + double wander; + double length; +}; + +#define NUM_STAGES 3 + +static struct stage stages[NUM_STAGES]; + +/* Enabled/disabled smoothing */ +static int enabled; + +/* Enabled/disabled mode where only leap seconds are smoothed out and normal + offset/frequency changes are ignored */ +static int leap_only_mode; + +/* Maximum skew/max_wander ratio to start updating offset and frequency */ +#define UNLOCK_SKEW_WANDER_RATIO 10000 + +static int locked; + +/* Maximum wander and frequency offset */ +static double max_wander; +static double max_freq; + +/* Frequency offset, time offset and the time of the last smoothing update */ +static double smooth_freq; +static double smooth_offset; +static struct timespec last_update; + + +static void +get_smoothing(struct timespec *now, double *poffset, double *pfreq, + double *pwander) +{ + double elapsed, length, offset, freq, wander; + int i; + + elapsed = UTI_DiffTimespecsToDouble(now, &last_update); + + offset = smooth_offset; + freq = smooth_freq; + wander = 0.0; + + for (i = 0; i < NUM_STAGES; i++) { + if (elapsed <= 0.0) + break; + + length = stages[i].length; + if (length >= elapsed) + length = elapsed; + + wander = stages[i].wander; + offset -= length * (2.0 * freq + wander * length) / 2.0; + freq += wander * length; + elapsed -= length; + } + + if (elapsed > 0.0) { + wander = 0.0; + offset -= elapsed * freq; + } + + *poffset = offset; + *pfreq = freq; + if (pwander) + *pwander = wander; +} + +static void +update_stages(void) +{ + double s1, s2, s, l1, l2, l3, lc, f, f2, l1t[2], l3t[2], err[2]; + int i, dir; + + /* Prepare the three stages so that the integral of the frequency offset + is equal to the offset that should be smoothed out */ + + s1 = smooth_offset / max_wander; + s2 = SQUARE(smooth_freq) / (2.0 * SQUARE(max_wander)); + + /* Calculate the lengths of the 1st and 3rd stage assuming there is no + frequency limit. The direction of the 1st stage is selected so that + the lengths will not be negative. With extremely small offsets both + directions may give a negative length due to numerical errors, so select + the one which gives a smaller error. */ + + for (i = 0, dir = -1; i <= 1; i++, dir += 2) { + err[i] = 0.0; + s = dir * s1 + s2; + + if (s < 0.0) { + err[i] += -s; + s = 0.0; + } + + l3t[i] = sqrt(s); + l1t[i] = l3t[i] - dir * smooth_freq / max_wander; + + if (l1t[i] < 0.0) { + err[i] += l1t[i] * l1t[i]; + l1t[i] = 0.0; + } + } + + if (err[0] < err[1]) { + l1 = l1t[0]; + l3 = l3t[0]; + dir = -1; + } else { + l1 = l1t[1]; + l3 = l3t[1]; + dir = 1; + } + + l2 = 0.0; + + /* If the limit was reached, shorten 1st+3rd stages and set a 2nd stage */ + f = dir * smooth_freq + l1 * max_wander - max_freq; + if (f > 0.0) { + lc = f / max_wander; + + /* No 1st stage if the frequency is already above the maximum */ + if (lc > l1) { + lc = l1; + f2 = dir * smooth_freq; + } else { + f2 = max_freq; + } + + l2 = lc * (2.0 + f / f2); + l1 -= lc; + l3 -= lc; + } + + stages[0].wander = dir * max_wander; + stages[0].length = l1; + stages[1].wander = 0.0; + stages[1].length = l2; + stages[2].wander = -dir * max_wander; + stages[2].length = l3; + + for (i = 0; i < NUM_STAGES; i++) { + DEBUG_LOG("Smooth stage %d wander %e length %f", + i + 1, stages[i].wander, stages[i].length); + } +} + +static void +update_smoothing(struct timespec *now, double offset, double freq) +{ + /* Don't accept offset/frequency until the clock has stabilized */ + if (locked) { + if (REF_GetSkew() / max_wander < UNLOCK_SKEW_WANDER_RATIO || leap_only_mode) + SMT_Activate(now); + return; + } + + get_smoothing(now, &smooth_offset, &smooth_freq, NULL); + smooth_offset += offset; + smooth_freq = (smooth_freq - freq) / (1.0 - freq); + last_update = *now; + + update_stages(); + + DEBUG_LOG("Smooth offset %e freq %e", smooth_offset, smooth_freq); +} + +static void +handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq, + double doffset, LCL_ChangeType change_type, void *anything) +{ + double delta; + + if (change_type == LCL_ChangeAdjust) { + if (leap_only_mode) + update_smoothing(cooked, 0.0, 0.0); + else + update_smoothing(cooked, doffset, dfreq); + } + + if (!UTI_IsZeroTimespec(&last_update)) + UTI_AdjustTimespec(&last_update, cooked, &last_update, &delta, dfreq, doffset); +} + +void SMT_Initialise(void) +{ + CNF_GetSmooth(&max_freq, &max_wander, &leap_only_mode); + if (max_freq <= 0.0 || max_wander <= 0.0) { + enabled = 0; + return; + } + + enabled = 1; + locked = 1; + + /* Convert from ppm */ + max_freq *= 1e-6; + max_wander *= 1e-6; + + UTI_ZeroTimespec(&last_update); + + LCL_AddParameterChangeHandler(handle_slew, NULL); +} + +void SMT_Finalise(void) +{ +} + +int SMT_IsEnabled(void) +{ + return enabled; +} + +double +SMT_GetOffset(struct timespec *now) +{ + double offset, freq; + + if (!enabled) + return 0.0; + + get_smoothing(now, &offset, &freq, NULL); + + return offset; +} + +void +SMT_Activate(struct timespec *now) +{ + if (!enabled || !locked) + return; + + LOG(LOGS_INFO, "Time smoothing activated%s", leap_only_mode ? + " (leap seconds only)" : ""); + locked = 0; + last_update = *now; +} + +void +SMT_Reset(struct timespec *now) +{ + int i; + + if (!enabled) + return; + + smooth_offset = 0.0; + smooth_freq = 0.0; + last_update = *now; + + for (i = 0; i < NUM_STAGES; i++) + stages[i].wander = stages[i].length = 0.0; +} + +void +SMT_Leap(struct timespec *now, int leap) +{ + /* When the leap-only mode is disabled, the leap second will be accumulated + in handle_slew() as a normal offset */ + if (!enabled || !leap_only_mode) + return; + + update_smoothing(now, leap, 0.0); +} + +int +SMT_GetSmoothingReport(RPT_SmoothingReport *report, struct timespec *now) +{ + double length, elapsed; + int i; + + if (!enabled) + return 0; + + report->active = !locked; + report->leap_only = leap_only_mode; + + get_smoothing(now, &report->offset, &report->freq_ppm, &report->wander_ppm); + + /* Convert to ppm and negate (positive values mean faster/speeding up) */ + report->freq_ppm *= -1.0e6; + report->wander_ppm *= -1.0e6; + + elapsed = UTI_DiffTimespecsToDouble(now, &last_update); + if (!locked && elapsed >= 0.0) { + for (i = 0, length = 0.0; i < NUM_STAGES; i++) + length += stages[i].length; + report->last_update_ago = elapsed; + report->remaining_time = elapsed < length ? length - elapsed : 0.0; + } else { + report->last_update_ago = 0.0; + report->remaining_time = 0.0; + } + + return 1; +} |