From 17c38b7490b3f0300c7812aefdae2ddda7ab4112 Mon Sep 17 00:00:00 2001 From: john stultz Date: Tue, 24 Jul 2007 18:38:34 -0700 Subject: 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 Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Linus Torvalds --- kernel/time/timekeeping.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) (limited to 'kernel/time/timekeeping.c') diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 07a3f1420c2..acc417b5a9b 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -47,10 +47,22 @@ EXPORT_SYMBOL(xtime_lock); struct timespec xtime __attribute__ ((aligned (16))); struct timespec wall_to_monotonic __attribute__ ((aligned (16))); static unsigned long total_sleep_time; /* seconds */ - EXPORT_SYMBOL(xtime); +#ifdef CONFIG_NO_HZ +static struct timespec xtime_cache __attribute__ ((aligned (16))); +static inline void update_xtime_cache(u64 nsec) +{ + xtime_cache = xtime; + timespec_add_ns(&xtime_cache, nsec); +} +#else +#define xtime_cache xtime +/* We do *not* want to evaluate the argument for this case */ +#define update_xtime_cache(n) do { } while (0) +#endif + static struct clocksource *clock; /* pointer to current clocksource */ @@ -478,6 +490,8 @@ void update_wall_time(void) xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift; clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; + update_xtime_cache(cyc2ns(clock, offset)); + /* check to see if there is a new clocksource to use */ change_clocksource(); update_vsyscall(&xtime, clock); @@ -510,6 +524,13 @@ void monotonic_to_bootbased(struct timespec *ts) ts->tv_sec += total_sleep_time; } +unsigned long get_seconds(void) +{ + return xtime_cache.tv_sec; +} +EXPORT_SYMBOL(get_seconds); + + struct timespec current_kernel_time(void) { struct timespec now; @@ -518,10 +539,9 @@ struct timespec current_kernel_time(void) do { seq = read_seqbegin(&xtime_lock); - now = xtime; + now = xtime_cache; } while (read_seqretry(&xtime_lock, seq)); return now; } - EXPORT_SYMBOL(current_kernel_time); -- cgit v1.2.3-18-g5258