[PATCH] ntp: prescale time_offset

This converts time_offset into a scaled per tick value.  This avoids now
completely the crude compensation in second_overflow().

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 17 insertions, 49 deletions

diff --git a/include/linux/timex.h b/include/linux/timex.h
index b589c8218bb9..1cde6f6a2712 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -89,7 +89,7 @@
  * FINENSEC is 1 ns in SHIFT_UPDATE units of the time_phase variable.
  */
 #define SHIFT_SCALE 22          /* phase scale (shift) */
-#define SHIFT_UPDATE (SHIFT_KG + MAXTC) /* time offset scale (shift) */
+#define SHIFT_UPDATE (SHIFT_HZ + 1) /* time offset scale (shift) */
 #define SHIFT_USEC 16           /* frequency offset scale (shift) */
 #define FINENSEC (1L << (SHIFT_SCALE - 10)) /* ~1 ns in phase units */
 
diff --git a/kernel/time/ntp.c b/kernel/time/ntp.c
index ab21eb06e09b..238ce47ef09d 100644
--- a/kernel/time/ntp.c
+++ b/kernel/time/ntp.c
@@ -31,7 +31,7 @@ int tickadj = 500/HZ ? : 1;		/* microsecs */
 /* TIME_ERROR prevents overwriting the CMOS clock */
 int time_state = TIME_OK;               /* clock synchronization status */
 int time_status = STA_UNSYNC;           /* clock status bits            */
-long time_offset;                       /* time adjustment (us)         */
+long time_offset;                       /* time adjustment (ns)         */
 long time_constant = 2;                 /* pll time constant            */
 long time_tolerance = MAXFREQ;          /* frequency tolerance (ppm)    */
 long time_precision = 1;                /* clock precision (us)         */
@@ -57,6 +57,7 @@ void ntp_clear(void)
         ntp_update_frequency();
 
         tick_length = tick_length_base;
+        time_offset = 0;
 }
 
 #define CLOCK_TICK_OVERFLOW     (LATCH * HZ - CLOCK_TICK_RATE)
@@ -83,7 +84,7 @@ void ntp_update_frequency(void)
  */
 void second_overflow(void)
 {
-        long ltemp, time_adj;
+        long time_adj;
 
         /* Bump the maxerror field */
         time_maxerror += time_tolerance >> SHIFT_USEC;
@@ -151,42 +152,14 @@ void second_overflow(void)
          * adjustment for each second is clamped so as to spread the adjustment
          * over not more than the number of seconds between updates.
          */
-        ltemp = time_offset;
-        if (!(time_status & STA_FLL))
-                ltemp = shift_right(ltemp, SHIFT_KG + time_constant);
-        ltemp = min(ltemp, (MAXPHASE / MINSEC) << SHIFT_UPDATE);
-        ltemp = max(ltemp, -(MAXPHASE / MINSEC) << SHIFT_UPDATE);
-        time_offset -= ltemp;
-        time_adj = ltemp << (SHIFT_SCALE - SHIFT_HZ - SHIFT_UPDATE);
-
-        /*
-         * Compute the frequency estimate and additional phase adjustment due
-         * to frequency error for the next second.
-         */
-
-#if HZ == 100
-        /*
-         * Compensate for (HZ==100) != (1 << SHIFT_HZ).  Add 25% and 3.125% to
-         * get 128.125; => only 0.125% error (p. 14)
-         */
-        time_adj += shift_right(time_adj, 2) + shift_right(time_adj, 5);
-#endif
-#if HZ == 250
-        /*
-         * Compensate for (HZ==250) != (1 << SHIFT_HZ).  Add 1.5625% and
-         * 0.78125% to get 255.85938; => only 0.05% error (p. 14)
-         */
-        time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
-#endif
-#if HZ == 1000
-        /*
-         * Compensate for (HZ==1000) != (1 << SHIFT_HZ).  Add 1.5625% and
-         * 0.78125% to get 1023.4375; => only 0.05% error (p. 14)
-         */
-        time_adj += shift_right(time_adj, 6) + shift_right(time_adj, 7);
-#endif
         tick_length = tick_length_base;
-        tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - (SHIFT_SCALE - 10));
+        time_adj = time_offset;
+        if (!(time_status & STA_FLL))
+                time_adj = shift_right(time_adj, SHIFT_KG + time_constant);
+        time_adj = min(time_adj, -((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
+        time_adj = max(time_adj, ((MAXPHASE / HZ) << SHIFT_UPDATE) / MINSEC);
+        time_offset -= time_adj;
+        tick_length += (s64)time_adj << (TICK_LENGTH_SHIFT - SHIFT_UPDATE);
 }
 
 /*
@@ -347,12 +320,8 @@ int do_adjtimex(struct timex *txc)
                      * Scale the phase adjustment and
                      * clamp to the operating range.
                      */
-                    if (ltemp > MAXPHASE)
-                        time_offset = MAXPHASE << SHIFT_UPDATE;
-                    else if (ltemp < -MAXPHASE)
-                        time_offset = -(MAXPHASE << SHIFT_UPDATE);
-                    else
-                        time_offset = ltemp << SHIFT_UPDATE;
+                    time_offset = min(ltemp, MAXPHASE);
+                    time_offset = max(time_offset, -MAXPHASE);
 
                     /*
                      * Select whether the frequency is to be controlled
@@ -366,8 +335,7 @@ int do_adjtimex(struct timex *txc)
                     time_reftime = xtime.tv_sec;
                     if (time_status & STA_FLL) {
                         if (mtemp >= MINSEC) {
-                            ltemp = (time_offset / mtemp) << (SHIFT_USEC -
-                                                              SHIFT_UPDATE);
+                            ltemp = ((time_offset << 12) / mtemp) << (SHIFT_USEC - 12);
                             time_freq += shift_right(ltemp, SHIFT_KH);
                         } else /* calibration interval too short (p. 12) */
                                 result = TIME_ERROR;
@@ -382,6 +350,7 @@ int do_adjtimex(struct timex *txc)
                     }
                     time_freq = min(time_freq, time_tolerance);
                     time_freq = max(time_freq, -time_tolerance);
+                    time_offset = (time_offset * NSEC_PER_USEC / HZ) << SHIFT_UPDATE;
                 } /* STA_PLL */
             } /* txc->modes & ADJ_OFFSET */
             if (txc->modes & ADJ_TICK)
@@ -395,9 +364,8 @@ leave:	if ((time_status & (STA_UNSYNC|STA_CLOCKERR)) != 0)
 
         if ((txc->modes & ADJ_OFFSET_SINGLESHOT) == ADJ_OFFSET_SINGLESHOT)
             txc->offset    = save_adjust;
-        else {
-            txc->offset = shift_right(time_offset, SHIFT_UPDATE);
-        }
+        else
+            txc->offset    = shift_right(time_offset, SHIFT_UPDATE) * HZ / 1000;
         txc->freq          = time_freq;
         txc->maxerror      = time_maxerror;
         txc->esterror      = time_esterror;