From 20d2363fb77ca506a35ce5de3ff10e63d37a2237 Mon Sep 17 00:00:00 2001
From: Miroslav Lichvar <mlichvar@redhat.com>
Date: Thu, 5 Jun 2014 14:46:22 +0200
Subject: [PATCH] reference: rework makestep

Rework makestep to cancel accumulated offset and step with the new
offset instead of accumulating new offset first, canceling all
accumulated offset and making the step.

This avoids two large frequency changes to initiate and cancel a slew
before making the step.
---
 cmdmon.c    |  2 +-
 local.c     |  9 +++------
 local.h     |  2 +-
 reference.c | 34 +++++++++++++++++++++++-----------
 4 files changed, 28 insertions(+), 19 deletions(-)

diff --git a/cmdmon.c b/cmdmon.c
index fe31406..1e27185 100644
--- a/cmdmon.c
+++ b/cmdmon.c
@@ -1589,7 +1589,7 @@ handle_manual_delete(CMD_Request *rx_message, CMD_Reply *tx_message)
 static void
 handle_make_step(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
-  LCL_MakeStep(0.0);
+  LCL_MakeStep();
   tx_message->status = htons(STT_SUCCESS);
 }
 
diff --git a/local.c b/local.c
index 158aa0c..f3cec54 100644
--- a/local.c
+++ b/local.c
@@ -563,10 +563,10 @@ lcl_RegisterSystemDrivers(lcl_ReadFrequencyDriver read_freq,
 
 /* ================================================== */
 /* Look at the current difference between the system time and the NTP
-   time, and make a step to cancel it if it's larger than the threshold. */
+   time, and make a step to cancel it. */
 
 int
-LCL_MakeStep(double threshold)
+LCL_MakeStep(void)
 {
   struct timeval raw;
   double correction;
@@ -574,14 +574,11 @@ LCL_MakeStep(double threshold)
   LCL_ReadRawTime(&raw);
   LCL_GetOffsetCorrection(&raw, &correction, NULL);
 
-  if (fabs(correction) <= threshold)
-    return 0;
-
   /* Cancel remaining slew and make the step */
   LCL_AccumulateOffset(correction, 0.0);
   LCL_ApplyStepOffset(-correction);
 
-  LOG(LOGS_WARN, LOGF_Local, "System clock was stepped by %.3f seconds", correction);
+  LOG(LOGS_WARN, LOGF_Local, "System clock was stepped by %.6f seconds", correction);
 
   return 1;
 }
diff --git a/local.h b/local.h
index 4000acd..6209510 100644
--- a/local.h
+++ b/local.h
@@ -189,7 +189,7 @@ extern void LCL_Finalise(void);
 /* Routine to convert the outstanding system clock error to a step and
    apply it, e.g. if the system clock has ended up an hour wrong due
    to a timezone problem. */
-extern int LCL_MakeStep(double threshold);
+extern int LCL_MakeStep(void);
 
 /* Routine to schedule a leap second. Leap second will be inserted
    at the end of the day if argument is positive, deleted if negative,
diff --git a/reference.c b/reference.c
index 80acc6f..160ac82 100644
--- a/reference.c
+++ b/reference.c
@@ -553,15 +553,15 @@ maybe_log_offset(double offset, time_t now)
 
 /* ================================================== */
 
-static void
-maybe_make_step()
+static int
+is_step_limit_reached(double offset, double offset_correction)
 {
   if (make_step_limit == 0) {
-    return;
+    return 0;
   } else if (make_step_limit > 0) {
     make_step_limit--;
   }
-  LCL_MakeStep(make_step_threshold);
+  return fabs(offset - offset_correction) > make_step_threshold;
 }
 
 /* ================================================== */
@@ -790,7 +790,7 @@ REF_SetReference(int stratum,
   double update_interval;
   double elapsed;
   double correction_rate;
-  double uncorrected_offset;
+  double uncorrected_offset, accumulate_offset, step_offset;
   struct timeval now, raw_now;
 
   assert(initialised);
@@ -868,6 +868,16 @@ REF_SetReference(int stratum,
 
   correction_rate = correction_time_ratio * 0.5 * offset_sd * update_interval;
 
+  /* Check if the clock should be stepped */
+  if (is_step_limit_reached(our_offset, uncorrected_offset)) {
+    /* Cancel the uncorrected offset and correct the total offset by step */
+    accumulate_offset = uncorrected_offset;
+    step_offset = our_offset - uncorrected_offset;
+  } else {
+    accumulate_offset = our_offset;
+    step_offset = 0.0;
+  }
+
   /* Eliminate updates that are based on totally unreliable frequency
      information. Ignore this limit with manual reference. */
 
@@ -902,21 +912,23 @@ REF_SetReference(int stratum,
 
     our_residual_freq = new_freq - our_frequency;
 
-    LCL_AccumulateFrequencyAndOffset(our_frequency, our_offset, correction_rate);
+    LCL_AccumulateFrequencyAndOffset(our_frequency, accumulate_offset, correction_rate);
     
   } else {
+    DEBUG_LOG(LOGF_Reference, "Skew %f too large to track, offset=%f", skew, accumulate_offset);
 
-#if 0    
-    LOG(LOGS_INFO, LOGF_Reference, "Skew %f too large to track, offset=%f", skew, our_offset);
-#endif
-    LCL_AccumulateOffset(our_offset, correction_rate);
+    LCL_AccumulateOffset(accumulate_offset, correction_rate);
 
     our_residual_freq = frequency;
   }
 
   update_leap_status(leap, raw_now.tv_sec);
   maybe_log_offset(our_offset, raw_now.tv_sec);
-  maybe_make_step();
+
+  if (step_offset != 0.0) {
+    LCL_ApplyStepOffset(step_offset);
+    LOG(LOGS_WARN, LOGF_Reference, "System clock was stepped by %.6f seconds", -step_offset);
+  }
 
   abs_freq_ppm = LCL_ReadAbsoluteFrequency();