2 files changed, 37 insertions, 5 deletions

diff --git a/include/linux/timex.h b/include/linux/timex.h
index 04a4a8cb4ed3..b7ca1204e42a 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -345,6 +345,9 @@ time_interpolator_reset(void)
 
 #endif /* !CONFIG_TIME_INTERPOLATION */
 
+/* Returns how long ticks are at present, in ns / 2^(SHIFT_SCALE-10). */
+extern u64 current_tick_length(void);
+
 #endif /* KERNEL */
 
 #endif /* LINUX_TIMEX_H */
diff --git a/kernel/timer.c b/kernel/timer.c
index b9dad3994676..fe3a9a9f8328 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -717,12 +717,16 @@ static void second_overflow(void)
 #endif
 }
 
-/* in the NTP reference this is called "hardclock()" */
-static void update_wall_time_one_tick(void)
+/*
+ * Returns how many microseconds we need to add to xtime this tick
+ * in doing an adjustment requested with adjtime.
+ */
+static long adjtime_adjustment(void)
 {
-        long time_adjust_step, delta_nsec;
+        long time_adjust_step;
 
-        if ((time_adjust_step = time_adjust) != 0 ) {
+        time_adjust_step = time_adjust;
+        if (time_adjust_step) {
                 /*
                  * We are doing an adjtime thing.  Prepare time_adjust_step to
                  * be within bounds.  Note that a positive time_adjust means we
@@ -733,10 +737,19 @@ static void update_wall_time_one_tick(void)
                  */
                 time_adjust_step = min(time_adjust_step, (long)tickadj);
                 time_adjust_step = max(time_adjust_step, (long)-tickadj);
+        }
+        return time_adjust_step;
+}
 
+/* in the NTP reference this is called "hardclock()" */
+static void update_wall_time_one_tick(void)
+{
+        long time_adjust_step, delta_nsec;
+
+        time_adjust_step = adjtime_adjustment();
+        if (time_adjust_step)
                 /* Reduce by this step the amount of time left  */
                 time_adjust -= time_adjust_step;
-        }
         delta_nsec = tick_nsec + time_adjust_step * 1000;
         /*
          * Advance the phase, once it gets to one microsecond, then
@@ -759,6 +772,22 @@ static void update_wall_time_one_tick(void)
 }
 
 /*
+ * Return how long ticks are at the moment, that is, how much time
+ * update_wall_time_one_tick will add to xtime next time we call it
+ * (assuming no calls to do_adjtimex in the meantime).
+ * The return value is in fixed-point nanoseconds with SHIFT_SCALE-10
+ * bits to the right of the binary point.
+ * This function has no side-effects.
+ */
+u64 current_tick_length(void)
+{
+        long delta_nsec;
+
+        delta_nsec = tick_nsec + adjtime_adjustment() * 1000;
+        return ((u64) delta_nsec << (SHIFT_SCALE - 10)) + time_adj;
+}
+
+/*
  * Using a loop looks inefficient, but "ticks" is
  * usually just one (we shouldn't be losing ticks,
  * we're doing this this way mainly for interrupt