diff options
author | john stultz <johnstul@us.ibm.com> | 2007-07-25 01:38:34 (GMT) |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-07-25 17:17:44 (GMT) |
commit | 17c38b7490b3f0300c7812aefdae2ddda7ab4112 (patch) | |
tree | 0f7a9ee0c691aef3497030e38c3ba8e3c13a985c /kernel/time | |
parent | 2c6b47de17c75d553de3e2fb426d8298d2074585 (diff) | |
download | linux-17c38b7490b3f0300c7812aefdae2ddda7ab4112.tar.xz |
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>
Diffstat (limited to 'kernel/time')
-rw-r--r-- | kernel/time/timekeeping.c | 26 |
1 files changed, 23 insertions, 3 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 07a3f14..acc417b 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); |