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authorIngo Molnar <mingo@elte.hu>2008-12-12 13:48:57 +0100
committerIngo Molnar <mingo@elte.hu>2008-12-12 13:48:57 +0100
commit45ab6b0c76d0e4cce5bd608ccf97b0f6b20f18df (patch)
tree4d51c73533c386aee16fde1e74b5e3bc22eedc53 /kernel/time
parent81444a799550214f549caf579cf65a0ca55e70b7 (diff)
parentd65bd5ecb2bd166cea4952a59b7e16cc3ad6ef6c (diff)
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Merge branch 'sched/core' into cpus4096
Conflicts: include/linux/ftrace.h kernel/sched.c
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/timekeeping.c22
1 files changed, 22 insertions, 0 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index e7acfb482a68..fa05e88aa76f 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -518,6 +518,28 @@ void update_wall_time(void)
/* correct the clock when NTP error is too big */
clocksource_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 clocksource_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)clock->xtime_nsec < 0)) {
+ s64 neg = -(s64)clock->xtime_nsec;
+ clock->xtime_nsec = 0;
+ clock->error += neg << (NTP_SCALE_SHIFT - clock->shift);
+ }
+
/* store full nanoseconds into xtime after rounding it up and
* add the remainder to the error difference.
*/