timekeeping: Add xtime_shift and ntp_error_shift to struct timekeeper

The xtime_nsec value in the timekeeper structure is shifted by a few
bits to improve precision. This happens to be the same value as the
clock->shift. To improve readability add xtime_shift to the timekeeper
and use it instead of the clock->shift. Likewise add ntp_error_shift
and replace all (NTP_SCALE_SHIFT - clock->shift) expressions.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134809.871899606@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 19 insertions, 14 deletions

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 7af45cbf6b13..dfdab1cefe1e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -23,6 +23,8 @@
 struct timekeeper {
         /* Current clocksource used for timekeeping. */
         struct clocksource *clock;
+        /* The shift value of the current clocksource. */
+        int     shift;
 
         /* Number of clock cycles in one NTP interval. */
         cycle_t cycle_interval;
@@ -36,6 +38,9 @@ struct timekeeper {
         /* Difference between accumulated time and NTP time in ntp
          * shifted nano seconds. */
         s64     ntp_error;
+        /* Shift conversion between clock shifted nano seconds and
+         * ntp shifted nano seconds. */
+        int     ntp_error_shift;
 };
 
 struct timekeeper timekeeper;
@@ -75,8 +80,10 @@ static void timekeeper_setup_internals(struct clocksource *clock)
                 ((u64) interval * clock->mult_orig) >> clock->shift;
 
         timekeeper.xtime_nsec = 0;
+        timekeeper.shift = clock->shift;
 
         timekeeper.ntp_error = 0;
+        timekeeper.ntp_error_shift = NTP_SCALE_SHIFT - clock->shift;
 }
 
 /*
@@ -641,8 +648,7 @@ static __always_inline int timekeeping_bigadjust(s64 error, s64 *interval,
          * Now calculate the error in (1 << look_ahead) ticks, but first
          * remove the single look ahead already included in the error.
          */
-        tick_error = tick_length >>
-                        (NTP_SCALE_SHIFT - timekeeper.clock->shift + 1);
+        tick_error = tick_length >> (timekeeper.ntp_error_shift + 1);
         tick_error -= timekeeper.xtime_interval >> 1;
         error = ((error - tick_error) >> look_ahead) + tick_error;
 
@@ -673,8 +679,7 @@ static void timekeeping_adjust(s64 offset)
         s64 error, interval = timekeeper.cycle_interval;
         int adj;
 
-        error = timekeeper.ntp_error >>
-                (NTP_SCALE_SHIFT - timekeeper.clock->shift - 1);
+        error = timekeeper.ntp_error >> (timekeeper.ntp_error_shift - 1);
         if (error > interval) {
                 error >>= 2;
                 if (likely(error <= interval))
@@ -696,7 +701,7 @@ static void timekeeping_adjust(s64 offset)
         timekeeper.xtime_interval += interval;
         timekeeper.xtime_nsec -= offset;
         timekeeper.ntp_error -= (interval - offset) <<
-                        (NTP_SCALE_SHIFT - timekeeper.clock->shift);
+                                timekeeper.ntp_error_shift;
 }
 
 /**
@@ -708,7 +713,7 @@ void update_wall_time(void)
 {
         struct clocksource *clock;
         cycle_t offset;
-        s64 nsecs;
+        u64 nsecs;
 
         /* Make sure we're fully resumed: */
         if (unlikely(timekeeping_suspended))
@@ -720,13 +725,13 @@ void update_wall_time(void)
 #else
         offset = timekeeper.cycle_interval;
 #endif
-        timekeeper.xtime_nsec = (s64)xtime.tv_nsec << clock->shift;
+        timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift;
 
         /* normally this loop will run just once, however in the
          * case of lost or late ticks, it will accumulate correctly.
          */
         while (offset >= timekeeper.cycle_interval) {
-                u64 nsecps = (u64)NSEC_PER_SEC << clock->shift;
+                u64 nsecps = (u64)NSEC_PER_SEC << timekeeper.shift;
 
                 /* accumulate one interval */
                 offset -= timekeeper.cycle_interval;
@@ -748,7 +753,7 @@ void update_wall_time(void)
                 /* accumulate error between NTP and clock interval */
                 timekeeper.ntp_error += tick_length;
                 timekeeper.ntp_error -= timekeeper.xtime_interval <<
-                                        (NTP_SCALE_SHIFT - clock->shift);
+                                        timekeeper.ntp_error_shift;
         }
 
         /* correct the clock when NTP error is too big */
@@ -773,16 +778,16 @@ void update_wall_time(void)
         if (unlikely((s64)timekeeper.xtime_nsec < 0)) {
                 s64 neg = -(s64)timekeeper.xtime_nsec;
                 timekeeper.xtime_nsec = 0;
-                timekeeper.ntp_error += neg << (NTP_SCALE_SHIFT - clock->shift);
+                timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;
         }
 
         /* store full nanoseconds into xtime after rounding it up and
          * add the remainder to the error difference.
          */
-        xtime.tv_nsec = ((s64)timekeeper.xtime_nsec >> clock->shift) + 1;
-        timekeeper.xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
-        timekeeper.ntp_error += timekeeper.xtime_nsec <<
-                                (NTP_SCALE_SHIFT - clock->shift);
+        xtime.tv_nsec = ((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
+        timekeeper.xtime_nsec -= (s64) xtime.tv_nsec << timekeeper.shift;
+        timekeeper.ntp_error += timekeeper.xtime_nsec <<
+                                timekeeper.ntp_error_shift;
 
         nsecs = clocksource_cyc2ns(offset, clock->mult, clock->shift);
         update_xtime_cache(nsecs);