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Subject[tip:timers/core] time: Move xtime_nsec adjustment underflow handling timekeeping_adjust
Commit-ID:  2a8c0883c3cfffcc148ea606e2a4e7453cd75e73
Gitweb: http://git.kernel.org/tip/2a8c0883c3cfffcc148ea606e2a4e7453cd75e73
Author: John Stultz <john.stultz@linaro.org>
AuthorDate: Fri, 13 Jul 2012 01:21:56 -0400
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 15 Jul 2012 10:39:07 +0200

time: Move xtime_nsec adjustment underflow handling timekeeping_adjust

When we make adjustments speeding up the clock, its possible
for xtime_nsec to underflow. We already handle this properly,
but we do so from update_wall_time() instead of the more logical
timekeeping_adjust(), where the possible underflow actually
occurs.

Thus, move the correction logic to the timekeeping_adjust, which
is the function that causes the issue. Making update_wall_time()
more readable.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Link: http://lkml.kernel.org/r/1342156917-25092-8-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/time/timekeeping.c | 42 +++++++++++++++++++++---------------------
1 files changed, 21 insertions(+), 21 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e43289d..aeeaab8 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -980,6 +980,27 @@ static void timekeeping_adjust(s64 offset)
timekeeper.xtime_nsec -= offset;
timekeeper.ntp_error -= (interval - offset) <<
timekeeper.ntp_error_shift;
+
+ /*
+ * It may be possible that when we entered this function, xtime_nsec
+ * was very small. Further, if we're slightly speeding the clocksource
+ * in the code above, its possible the required corrective factor to
+ * xtime_nsec could cause it to underflow.
+ *
+ * Now, since we already accumulated the second, cannot simply roll
+ * the accumulated second back, since the NTP subsystem has been
+ * notified via second_overflow. So instead we push xtime_nsec forward
+ * by the amount we underflowed, and add that amount into the error.
+ *
+ * We'll correct this error next time through this function, when
+ * xtime_nsec is not as small.
+ */
+ if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
+ s64 neg = -(s64)timekeeper.xtime_nsec;
+ timekeeper.xtime_nsec = 0;
+ timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
+ }
+
}


@@ -1105,27 +1126,6 @@ static void update_wall_time(void)
/* correct the clock when NTP error is too big */
timekeeping_adjust(offset);

- /*
- * Since in the loop above, we accumulate any amount of time
- * in xtime_nsec over a second into xtime.tv_sec, its possible for
- * xtime_nsec to be fairly small after the loop. Further, if we're
- * slightly speeding the clocksource up in timekeeping_adjust(),
- * its possible the required corrective factor to xtime_nsec could
- * cause it to underflow.
- *
- * Now, we cannot simply roll the accumulated second back, since
- * the NTP subsystem has been notified via second_overflow. So
- * instead we push xtime_nsec forward by the amount we underflowed,
- * and add that amount into the error.
- *
- * We'll correct this error next time through this function, when
- * xtime_nsec is not as small.
- */
- if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
- s64 neg = -(s64)timekeeper.xtime_nsec;
- timekeeper.xtime_nsec = 0;
- timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
- }

/*
* Store only full nanoseconds into xtime_nsec after rounding

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