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Cache xtime every call to update_wall_time

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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>
This commit is contained in:
john stultz
2007-07-24 18:38:34 -07:00
committed by Linus Torvalds
parent 2c6b47de17
commit 17c38b7490
3 changed files with 24 additions and 12 deletions
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6
include/linux/time.h
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@ -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())