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authorjohn stultz <johnstul@us.ibm.com>2007-07-24 21:38:34 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-25 13:17:44 -0400
commit17c38b7490b3f0300c7812aefdae2ddda7ab4112 (patch)
tree0f7a9ee0c691aef3497030e38c3ba8e3c13a985c /kernel/time
parent2c6b47de17c75d553de3e2fb426d8298d2074585 (diff)
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.c26
1 files changed, 23 insertions, 3 deletions
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);
47struct timespec xtime __attribute__ ((aligned (16))); 47struct timespec xtime __attribute__ ((aligned (16)));
48struct timespec wall_to_monotonic __attribute__ ((aligned (16))); 48struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
49static unsigned long total_sleep_time; /* seconds */ 49static unsigned long total_sleep_time; /* seconds */
50
51EXPORT_SYMBOL(xtime); 50EXPORT_SYMBOL(xtime);
52 51
53 52
53#ifdef CONFIG_NO_HZ
54static struct timespec xtime_cache __attribute__ ((aligned (16)));
55static inline void update_xtime_cache(u64 nsec)
56{
57 xtime_cache = xtime;
58 timespec_add_ns(&xtime_cache, nsec);
59}
60#else
61#define xtime_cache xtime
62/* We do *not* want to evaluate the argument for this case */
63#define update_xtime_cache(n) do { } while (0)
64#endif
65
54static struct clocksource *clock; /* pointer to current clocksource */ 66static struct clocksource *clock; /* pointer to current clocksource */
55 67
56 68
@@ -478,6 +490,8 @@ void update_wall_time(void)
478 xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift; 490 xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
479 clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift; 491 clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
480 492
493 update_xtime_cache(cyc2ns(clock, offset));
494
481 /* check to see if there is a new clocksource to use */ 495 /* check to see if there is a new clocksource to use */
482 change_clocksource(); 496 change_clocksource();
483 update_vsyscall(&xtime, clock); 497 update_vsyscall(&xtime, clock);
@@ -510,6 +524,13 @@ void monotonic_to_bootbased(struct timespec *ts)
510 ts->tv_sec += total_sleep_time; 524 ts->tv_sec += total_sleep_time;
511} 525}
512 526
527unsigned long get_seconds(void)
528{
529 return xtime_cache.tv_sec;
530}
531EXPORT_SYMBOL(get_seconds);
532
533
513struct timespec current_kernel_time(void) 534struct timespec current_kernel_time(void)
514{ 535{
515 struct timespec now; 536 struct timespec now;
@@ -518,10 +539,9 @@ struct timespec current_kernel_time(void)
518 do { 539 do {
519 seq = read_seqbegin(&xtime_lock); 540 seq = read_seqbegin(&xtime_lock);
520 541
521 now = xtime; 542 now = xtime_cache;
522 } while (read_seqretry(&xtime_lock, seq)); 543 } while (read_seqretry(&xtime_lock, seq));
523 544
524 return now; 545 return now;
525} 546}
526
527EXPORT_SYMBOL(current_kernel_time); 547EXPORT_SYMBOL(current_kernel_time);