Re: [PATCH 7/8] time: Move xtime_nsec adjustment underflow handling timekeeping_adjust
* John Stultz wrote: > 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. > > CC: Ingo Molnar > CC: Peter Zijlstra > CC: Richard Cochran > CC: Prarit Bhargava > CC: Thomas Gleixner > Signed-off-by: John Stultz > --- > kernel/time/timekeeping.c | 42 +- > 1 file changed, 21 insertions(+), 21 deletions(-) > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index dd119355..4b76432 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -987,6 +987,27 @@ 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. s/slightly speeding/slightly speeding up ? > + * > + * Now, since we already accumulated the second, cannot simply roll > + * the accumulated second back, since the NTP subsystem has been s/cannot/we cannot ? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH 7/8] time: Move xtime_nsec adjustment underflow handling timekeeping_adjust
* John Stultz john.stu...@linaro.org wrote: 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. CC: Ingo Molnar mi...@kernel.org CC: Peter Zijlstra a.p.zijls...@chello.nl CC: Richard Cochran richardcoch...@gmail.com CC: Prarit Bhargava pra...@redhat.com CC: Thomas Gleixner t...@linutronix.de Signed-off-by: John Stultz johns...@us.ibm.com --- kernel/time/timekeeping.c | 42 +- 1 file changed, 21 insertions(+), 21 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index dd119355..4b76432 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -987,6 +987,27 @@ 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. s/slightly speeding/slightly speeding up ? + * + * Now, since we already accumulated the second, cannot simply roll + * the accumulated second back, since the NTP subsystem has been s/cannot/we cannot ? Thanks, Ingo -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 7/8] 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.
CC: Ingo Molnar
CC: Peter Zijlstra
CC: Richard Cochran
CC: Prarit Bhargava
CC: Thomas Gleixner
Signed-off-by: John Stultz
---
kernel/time/timekeeping.c | 42 +-
1 file changed, 21 insertions(+), 21 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index dd119355..4b76432 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -987,6 +987,27 @@ 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;
+ }
+
}
@@ -1112,27 +1133,6 @@ 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
--
1.7.9.5
--
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[PATCH 7/8] 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.
CC: Ingo Molnar mi...@kernel.org
CC: Peter Zijlstra a.p.zijls...@chello.nl
CC: Richard Cochran richardcoch...@gmail.com
CC: Prarit Bhargava pra...@redhat.com
CC: Thomas Gleixner t...@linutronix.de
Signed-off-by: John Stultz johns...@us.ibm.com
---
kernel/time/timekeeping.c | 42 +-
1 file changed, 21 insertions(+), 21 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index dd119355..4b76432 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -987,6 +987,27 @@ 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;
+ }
+
}
@@ -1112,27 +1133,6 @@ 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
--
1.7.9.5
--
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Please read the FAQ at http://www.tux.org/lkml/
