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-rw-r--r--kernel/time/timekeeping.c85
1 files changed, 60 insertions, 25 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index fb0f46fa1ecd..5fdd78e0858a 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -721,6 +721,51 @@ static void timekeeping_adjust(s64 offset)
721 timekeeper.ntp_error_shift; 721 timekeeper.ntp_error_shift;
722} 722}
723 723
724
725/**
726 * logarithmic_accumulation - shifted accumulation of cycles
727 *
728 * This functions accumulates a shifted interval of cycles into
729 * into a shifted interval nanoseconds. Allows for O(log) accumulation
730 * loop.
731 *
732 * Returns the unconsumed cycles.
733 */
734static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
735{
736 u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;
737
738 /* If the offset is smaller then a shifted interval, do nothing */
739 if (offset < timekeeper.cycle_interval<<shift)
740 return offset;
741
742 /* Accumulate one shifted interval */
743 offset -= timekeeper.cycle_interval << shift;
744 timekeeper.clock->cycle_last += timekeeper.cycle_interval << shift;
745
746 timekeeper.xtime_nsec += timekeeper.xtime_interval << shift;
747 while (timekeeper.xtime_nsec >= nsecps) {
748 timekeeper.xtime_nsec -= nsecps;
749 xtime.tv_sec++;
750 second_overflow();
751 }
752
753 /* Accumulate into raw time */
754 raw_time.tv_nsec += timekeeper.raw_interval << shift;;
755 while (raw_time.tv_nsec >= NSEC_PER_SEC) {
756 raw_time.tv_nsec -= NSEC_PER_SEC;
757 raw_time.tv_sec++;
758 }
759
760 /* Accumulate error between NTP and clock interval */
761 timekeeper.ntp_error += tick_length << shift;
762 timekeeper.ntp_error -= timekeeper.xtime_interval <<
763 (timekeeper.ntp_error_shift + shift);
764
765 return offset;
766}
767
768
724/** 769/**
725 * update_wall_time - Uses the current clocksource to increment the wall time 770 * update_wall_time - Uses the current clocksource to increment the wall time
726 * 771 *
@@ -731,6 +776,7 @@ void update_wall_time(void)
731 struct clocksource *clock; 776 struct clocksource *clock;
732 cycle_t offset; 777 cycle_t offset;
733 u64 nsecs; 778 u64 nsecs;
779 int shift = 0, maxshift;
734 780
735 /* Make sure we're fully resumed: */ 781 /* Make sure we're fully resumed: */
736 if (unlikely(timekeeping_suspended)) 782 if (unlikely(timekeeping_suspended))
@@ -744,33 +790,22 @@ void update_wall_time(void)
744#endif 790#endif
745 timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift; 791 timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;
746 792
747 /* normally this loop will run just once, however in the 793 /*
748 * case of lost or late ticks, it will accumulate correctly. 794 * With NO_HZ we may have to accumulate many cycle_intervals
795 * (think "ticks") worth of time at once. To do this efficiently,
796 * we calculate the largest doubling multiple of cycle_intervals
797 * that is smaller then the offset. We then accumulate that
798 * chunk in one go, and then try to consume the next smaller
799 * doubled multiple.
749 */ 800 */
801 shift = ilog2(offset) - ilog2(timekeeper.cycle_interval);
802 shift = max(0, shift);
803 /* Bound shift to one less then what overflows tick_length */
804 maxshift = (8*sizeof(tick_length) - (ilog2(tick_length)+1)) - 1;
805 shift = min(shift, maxshift);
750 while (offset >= timekeeper.cycle_interval) { 806 while (offset >= timekeeper.cycle_interval) {
751 u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift; 807 offset = logarithmic_accumulation(offset, shift);
752 808 shift--;
753 /* accumulate one interval */
754 offset -= timekeeper.cycle_interval;
755 clock->cycle_last += timekeeper.cycle_interval;
756
757 timekeeper.xtime_nsec += timekeeper.xtime_interval;
758 if (timekeeper.xtime_nsec >= nsecps) {
759 timekeeper.xtime_nsec -= nsecps;
760 xtime.tv_sec++;
761 second_overflow();
762 }
763
764 raw_time.tv_nsec += timekeeper.raw_interval;
765 if (raw_time.tv_nsec >= NSEC_PER_SEC) {
766 raw_time.tv_nsec -= NSEC_PER_SEC;
767 raw_time.tv_sec++;
768 }
769
770 /* accumulate error between NTP and clock interval */
771 timekeeper.ntp_error += tick_length;
772 timekeeper.ntp_error -= timekeeper.xtime_interval <<
773 timekeeper.ntp_error_shift;
774 } 809 }
775 810
776 /* correct the clock when NTP error is too big */ 811 /* correct the clock when NTP error is too big */