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    Subject[patch 10/15] add xtime_shift and ntp_error_shift to struct timekeeper
    From: Martin Schwidefsky <schwidefsky@de.ibm.com>

    The xtime_nsec value in the timekeeper structure is shifted by a few
    bits to improve precision. This happens to be the same value as the
    clock->shift. To improve readability add xtime_shift to the timekeeper
    and use it instead of the clock->shift. Likewise add ntp_error_shift
    and replace all (NTP_SCALE_SHIFT - clock->shift) expressions.

    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: john stultz <johnstul@us.ibm.com>
    Cc: Daniel Walker <dwalker@fifo99.com>
    Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
    ---
    kernel/time/timekeeping.c | 36 +++++++++++++++++++++---------------
    1 file changed, 21 insertions(+), 15 deletions(-)

    Index: linux-2.6/kernel/time/timekeeping.c
    ===================================================================
    --- linux-2.6.orig/kernel/time/timekeeping.c
    +++ linux-2.6/kernel/time/timekeeping.c
    @@ -23,6 +23,8 @@
    struct timekeeper {
    /* Current clocksource used for timekeeping. */
    struct clocksource *clock;
    + /* The shift value of the current clocksource. */
    + int shift;

    /* Number of clock cycles in one NTP interval. */
    cycle_t cycle_interval;
    @@ -36,6 +38,9 @@ struct timekeeper {
    /* Difference between accumulated time and NTP time in ntp
    * shifted nano seconds. */
    s64 ntp_error;
    + /* Shift conversion between clock shifted nano seconds and
    + * ntp shifted nano seconds. */
    + int ntp_error_shift;
    };

    struct timekeeper timekeeper;
    @@ -75,8 +80,10 @@ static void timekeeper_setup_internals(s
    ((u64) interval * clock->mult_orig) >> clock->shift;

    timekeeper.xtime_nsec = 0;
    + timekeeper.shift = clock->shift;

    timekeeper.ntp_error = 0;
    + timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
    }

    /*
    @@ -641,8 +648,7 @@ static __always_inline int timekeeping_b
    * Now calculate the error in (1 << look_ahead) ticks, but first
    * remove the single look ahead already included in the error.
    */
    - tick_error = tick_length >>
    - (NTP_SCALE_SHIFT - timekeeper.clock->shift + 1);
    + tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
    tick_error -= timekeeper.xtime_interval >> 1;
    error = ((error - tick_error) >> look_ahead) + tick_error;

    @@ -673,8 +679,7 @@ static void timekeeping_adjust(s64 offse
    s64 error, interval = timekeeper.cycle_interval;
    int adj;

    - error = timekeeper.ntp_error >>
    - (NTP_SCALE_SHIFT - timekeeper.clock->shift - 1);
    + error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
    if (error > interval) {
    error >>= 2;
    if (likely(error <= interval))
    @@ -696,7 +701,7 @@ static void timekeeping_adjust(s64 offse
    timekeeper.xtime_interval += interval;
    timekeeper.xtime_nsec -= offset;
    timekeeper.ntp_error -= (interval - offset) <<
    - (NTP_SCALE_SHIFT - timekeeper.clock->shift);
    + timekeeper.ntp_error_shift;
    }

    /**
    @@ -708,7 +713,7 @@ void update_wall_time(void)
    {
    struct clocksource *clock;
    cycle_t offset;
    - s64 nsecs;
    + u64 nsecs;

    /* Make sure we're fully resumed: */
    if (unlikely(timekeeping_suspended))
    @@ -720,7 +725,7 @@ void update_wall_time(void)
    #else
    offset = timekeeper.cycle_interval;
    #endif
    - timekeeper.xtime_nsec = (s64)xtime.tv_nsec << clock->shift;
    + timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;

    /* normally this loop will run just once, however in the
    * case of lost or late ticks, it will accumulate correctly.
    @@ -731,8 +736,9 @@ void update_wall_time(void)
    clock->cycle_last += timekeeper.cycle_interval;

    timekeeper.xtime_nsec += timekeeper.xtime_interval;
    - if (timekeeper.xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
    - timekeeper.xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
    + nsecs = (u64) NSEC_PER_SEC << timekeeper.shift;
    + if (timekeeper.xtime_nsec >= nsecs) {
    + timekeeper.xtime_nsec -= nsecs;
    xtime.tv_sec++;
    second_overflow();
    }
    @@ -746,7 +752,7 @@ void update_wall_time(void)
    /* accumulate error between NTP and clock interval */
    timekeeper.ntp_error += tick_length;
    timekeeper.ntp_error -= timekeeper.xtime_interval <<
    - (NTP_SCALE_SHIFT - clock->shift);
    + timekeeper.ntp_error_shift;
    }

    /* correct the clock when NTP error is too big */
    @@ -771,16 +777,16 @@ void update_wall_time(void)
    if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
    s64 neg = -(s64)timekeeper.xtime_nsec;
    timekeeper.xtime_nsec = 0;
    - timekeeper.ntp_error += neg << (NTP_SCALE_SHIFT - clock->shift);
    + timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
    }

    /* store full nanoseconds into xtime after rounding it up and
    * add the remainder to the error difference.
    */
    - xtime.tv_nsec = ((s64)timekeeper.xtime_nsec >> clock->shift) + 1;
    - timekeeper.xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
    - timekeeper.ntp_error += timekeeper.xtime_nsec <<
    - (NTP_SCALE_SHIFT - clock->shift);
    + xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
    + timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
    + timekeeper.ntp_error += timekeeper.xtime_nsec <<
    + timekeeper.ntp_error_shift;

    nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);
    update_xtime_cache(nsecs);
    --
    blue skies,
    Martin.

    "Reality continues to ruin my life." - Calvin.



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