time: Only do nanosecond rounding on GENERIC_TIME_VSYSCALL_OLD systems (92bb1fcf) · Commits · 戴 / test

kernel/time/timekeeping.c

+31 −14

Original line number	Diff line number	Diff line
		@@ -1062,6 +1062,33 @@ static cycle_t logarithmic_accumulation(struct timekeeper *tk, cycle_t offset,
		return offset;
		}

		#ifdef CONFIG_GENERIC_TIME_VSYSCALL_OLD
		static inline void old_vsyscall_fixup(struct timekeeper *tk)
		{
		s64 remainder;

		/*
		* Store only full nanoseconds into xtime_nsec after rounding
		* it up and add the remainder to the error difference.
		* XXX - This is necessary to avoid small 1ns inconsistnecies caused
		* by truncating the remainder in vsyscalls. However, it causes
		* additional work to be done in timekeeping_adjust(). Once
		* the vsyscall implementations are converted to use xtime_nsec
		* (shifted nanoseconds), and CONFIG_GENERIC_TIME_VSYSCALL_OLD
		* users are removed, this can be killed.
		*/
		remainder = tk->xtime_nsec & ((1ULL << tk->shift) - 1);
		tk->xtime_nsec -= remainder;
		tk->xtime_nsec += 1ULL << tk->shift;
		tk->ntp_error += remainder << tk->ntp_error_shift;

		}
		#else
		#define old_vsyscall_fixup(tk)
		#endif



		/**
		* update_wall_time - Uses the current clocksource to increment the wall time
		*
		@@ -1073,7 +1100,6 @@ static void update_wall_time(void)
		cycle_t offset;
		int shift = 0, maxshift;
		unsigned long flags;
		s64 remainder;

		write_seqlock_irqsave(&tk->lock, flags);

		@@ -1115,20 +1141,11 @@ static void update_wall_time(void)
		/* correct the clock when NTP error is too big */
		timekeeping_adjust(tk, offset);


		/*
		* Store only full nanoseconds into xtime_nsec after rounding
		* it up and add the remainder to the error difference.
		* XXX - This is necessary to avoid small 1ns inconsistnecies caused
		* by truncating the remainder in vsyscalls. However, it causes
		* additional work to be done in timekeeping_adjust(). Once
		* the vsyscall implementations are converted to use xtime_nsec
		* (shifted nanoseconds), this can be killed.
		* XXX This can be killed once everyone converts
		* to the new update_vsyscall.
		*/
		remainder = tk->xtime_nsec & ((1ULL << tk->shift) - 1);
		tk->xtime_nsec -= remainder;
		tk->xtime_nsec += 1ULL << tk->shift;
		tk->ntp_error += remainder << tk->ntp_error_shift;
		old_vsyscall_fixup(tk);

		/*
		* Finally, make sure that after the rounding

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