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timekeeping: Provide hrtimer update function 

To finally fix the infamous leap second issue and other race windows
caused by functions which change the offsets between the various time
bases (CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_BOOTTIME) we need a
function which atomically gets the current monotonic time and updates
the offsets of CLOCK_REALTIME and CLOCK_BOOTTIME with minimalistic
overhead. The previous patch which provides ktime_t offsets allows us
to make this function almost as cheap as ktime_get() which is going to
be replaced in hrtimer_interrupt().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/1341960205-56738-7-git-send-email-johnstul@us.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Thomas Gleixner 2012-07-10 18:43:24 -04:00
parent 196951e912
commit f6c06abfb3
2 changed files with 35 additions and 0 deletions
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1
include/linux/hrtimer.h
View File

@ -327,6 +327,7 @@ extern ktime_t ktime_get(void);
extern ktime_t ktime_get_real(void); extern ktime_t ktime_get_real(void);
extern ktime_t ktime_get_boottime(void); extern ktime_t ktime_get_boottime(void);
extern ktime_t ktime_get_monotonic_offset(void); extern ktime_t ktime_get_monotonic_offset(void);
extern ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot);
DECLARE_PER_CPU(struct tick_device, tick_cpu_device); DECLARE_PER_CPU(struct tick_device, tick_cpu_device);

34
kernel/time/timekeeping.c
View File

@ -1271,6 +1271,40 @@ void get_xtime_and_monotonic_and_sleep_offset(struct timespec *xtim,
} while (read_seqretry(&timekeeper.lock, seq)); } while (read_seqretry(&timekeeper.lock, seq));
} }
#ifdef CONFIG_HIGH_RES_TIMERS
/**
* ktime_get_update_offsets - hrtimer helper
* @offs_real: pointer to storage for monotonic -> realtime offset
* @offs_boot: pointer to storage for monotonic -> boottime offset
*
* Returns current monotonic time and updates the offsets
* Called from hrtimer_interupt() or retrigger_next_event()
*/
ktime_t ktime_get_update_offsets(ktime_t *offs_real, ktime_t *offs_boot)
{
ktime_t now;
unsigned int seq;
u64 secs, nsecs;
do {
seq = read_seqbegin(&timekeeper.lock);
secs = timekeeper.xtime.tv_sec;
nsecs = timekeeper.xtime.tv_nsec;
nsecs += timekeeping_get_ns();
/* If arch requires, add in gettimeoffset() */
nsecs += arch_gettimeoffset();
*offs_real = timekeeper.offs_real;
*offs_boot = timekeeper.offs_boot;
} while (read_seqretry(&timekeeper.lock, seq));
now = ktime_add_ns(ktime_set(secs, 0), nsecs);
now = ktime_sub(now, *offs_real);
return now;
}
#endif
/** /**
* ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format * ktime_get_monotonic_offset() - get wall_to_monotonic in ktime_t format
*/ */