From: Martin Schwidefsky 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 Cc: Thomas Gleixner Cc: john stultz Cc: Daniel Walker Signed-off-by: Martin Schwidefsky --- kernel/time/timekeeping.c | 33 ++++++++++++++++++--------------- 1 file changed, 18 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 @@ -27,6 +27,8 @@ struct timekeeper { u32 raw_interval; u64 xtime_nsec; s64 ntp_error; + int xtime_shift; + int ntp_error_shift; }; struct timekeeper timekeeper; @@ -66,8 +68,10 @@ static void timekeeper_setup_internals(s ((u64) interval * clock->mult_orig) >> clock->shift; timekeeper.xtime_nsec = 0; + timekeeper.xtime_shift = clock->shift; timekeeper.ntp_error = 0; + timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift; } /* @@ -621,8 +625,7 @@ 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; @@ -653,8 +656,7 @@ 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)) @@ -676,7 +678,7 @@ 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; } /** @@ -688,7 +690,7 @@ 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)) @@ -700,7 +702,7 @@ 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.xtime_shift; /* normally this loop will run just once, however in the * case of lost or late ticks, it will accumulate correctly. @@ -711,8 +713,9 @@ 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.xtime_shift; + if (timekeeper.xtime_nsec >= nsecs) { + timekeeper.xtime_nsec -= nsecs; xtime.tv_sec++; second_overflow(); } @@ -726,7 +729,7 @@ 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 */ @@ -751,16 +754,16 @@ 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.xtime_shift) + 1; + timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.xtime_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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/