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timekeeping: Shorten seq_count region

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Shorten the seqcount write hold region to the actual update of the
timekeeper and the related data (e.g vsyscall).

On a contemporary x86 system this reduces the maximum latencies on
Preempt-RT from 8us to 4us on the non-timekeeping cores.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Thomas Gleixner 2013-02-21 22:51:40 +00:00 committed by John Stultz
parent 48cdc135d4
commit ca4523cda4
1 changed files with 2 additions and 3 deletions
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5
kernel/time/timekeeping.c
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@ -1341,7 +1341,6 @@ static void update_wall_time(void)
unsigned long flags;
raw_spin_lock_irqsave(&timekeeper_lock, flags);
write_seqcount_begin(&timekeeper_seq);
/* Make sure we're fully resumed: */
if (unlikely(timekeeping_suspended))
@ -1393,6 +1392,7 @@ static void update_wall_time(void)
*/
accumulate_nsecs_to_secs(tk);
write_seqcount_begin(&timekeeper_seq);
/* Update clock->cycle_last with the new value */
clock->cycle_last = tk->cycle_last;
/*
@ -1407,9 +1407,8 @@ static void update_wall_time(void)
*/
memcpy(real_tk, tk, sizeof(*tk));
timekeeping_update(real_tk, false, false);
out:
write_seqcount_end(&timekeeper_seq);
out:
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}