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    Subject[NTP 4/9] 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>
    ---
    include/linux/timex.h | 2 -
    kernel/time/ntp.c | 64 ++++++++++++--------------------------------------
    2 files changed, 17 insertions(+), 49 deletions(-)

    Index: linux-2.6-mm/include/linux/timex.h
    ===================================================================
    --- linux-2.6-mm.orig/include/linux/timex.h
    +++ linux-2.6-mm/include/linux/timex.h
    @@ -90,7 +90,7 @@
    * 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 */

    Index: linux-2.6-mm/kernel/time/ntp.c
    ===================================================================
    --- linux-2.6-mm.orig/kernel/time/ntp.c
    +++ linux-2.6-mm/kernel/time/ntp.c
    @@ -37,7 +37,7 @@ int tickadj = 500/HZ ? : 1; /* microsec
    /* 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) */
    @@ -63,6 +63,7 @@ void ntp_clear(void)
    ntp_update_frequency();

    tick_length = tick_length_base;
    + time_offset = 0;
    }

    #define CLOCK_TICK_OVERFLOW (LATCH * HZ - CLOCK_TICK_RATE)
    @@ -89,7 +90,7 @@ 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;
    @@ -157,42 +158,14 @@ 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);
    }

    /*
    @@ -353,12 +326,8 @@ 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
    @@ -372,8 +341,7 @@ 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;
    @@ -388,6 +356,7 @@ 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)
    @@ -401,9 +370,8 @@ leave: if ((time_status & (STA_UNSYNC|ST

    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;
    --

    -
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