Cache xtime every call to update_wall_time

This avoids xtime lag seen with dynticks, because while 'xtime' itself
is still not updated often, we keep a 'xtime_cache' variable around that
contains the approximate real-time that _is_ updated each time we do a
'update_wall_time()', and is thus never off by more than one tick.

IOW, this restores the original semantics for 'xtime' users, as long as
you use the proper abstraction functions (ie 'current_kernel_time()' or
'get_seconds()' depending on whether you want a timespec or just the
seconds field).

[ Updated Patch.  As penance for my sins I've also yanked another #ifdef
  that was added to avoid the xtime lag w/ hrtimers.  ]

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 5 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index 71181df8b744..6a5f503b4f1d 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -99,11 +99,7 @@ extern int update_persistent_clock(struct timespec now);
 extern int no_sync_cmos_clock __read_mostly;
 void timekeeping_init(void);
 
-static inline unsigned long get_seconds(void)
-{
-        return xtime.tv_sec;
-}
-
+unsigned long get_seconds(void);
 struct timespec current_kernel_time(void);
 
 #define CURRENT_TIME            (current_kernel_time())