[PATCH 3/10] Time: Let user request precision from current_tick_length()

john stultz
2006-03-23T03:06:35Z

Change the current_tick_length() function so it takes an
argument which specifies how much precision to return in shifted
nanoseconds. This provides a simple way to convert between NTPs
internal nanoseconds shifted by (SHIFT_SCALE - 10) to other shifted
nanosecond units that are used by the clocksource abstraction.

Signed-off-by John Stultz <johnstul@us.ibm.com>

arch/powerpc/kernel/time.c | 2 +-
include/linux/timex.h | 2 +-
kernel/timer.c | 21 +++++++++++++++++----
3 files changed, 19 insertions(+), 6 deletions(-)

linux-2.6.16_timeofday-core2_C1.patch
============================================
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 86f7e3d..08a53a4 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -315,7 +315,7 @@ static __inline__ void timer_recalc_offs

if (__USE_RTC())
return;
- tlen = current_tick_length();
+ tlen = current_tick_length(SHIFT_SCALE - 10);
offset = cur_tb - do_gtod.varp->tb_orig_stamp;
if (tlen == last_tick_len && offset < 0x80000000u)
return;
diff --git a/include/linux/timex.h b/include/linux/timex.h
index b7ca120..e239f2d 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -346,7 +346,7 @@ 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);
+extern u64 current_tick_length(long);

#endif /* KERNEL */

diff --git a/kernel/timer.c b/kernel/timer.c
index 78a9d03..dc9b4ec 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -791,16 +791,29 @@ static void update_wall_time_one_tick(vo
* 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.
+ * The return value is in fixed-point nanoseconds shifted by the
+ * specified number of bits to the right of the binary point.
* This function has no side-effects.
*/
-u64 current_tick_length(void)
+u64 current_tick_length(long shift)
{
long delta_nsec;
+ u64 ret;

+ /* calculate the finest interval NTP will allow.
+ * ie: nanosecond value shifted by (SHIFT_SCALE - 10)
+ */
delta_nsec = tick_nsec + adjtime_adjustment() * 1000;
- return ((u64) delta_nsec << (SHIFT_SCALE - 10)) + time_adj;
+ ret = ((u64) delta_nsec << (SHIFT_SCALE - 10)) + time_adj;
+
+ /* convert from (SHIFT_SCALE - 10) to specified shift scale: */
+ shift = shift - (SHIFT_SCALE - 10);
+ if (shift < 0)
+ ret >>= -shift;
+ else
+ ret <<= shift;
+
+ return ret;
}

/* XXX - all of this timekeeping code should be later moved to time.c */