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timekeeping: Implement a shadow timekeeper 

Use the shadow timekeeper to do the update_wall_time() adjustments and
then copy it over to the real timekeeper.

Keep the shadow timekeeper in sync when updating stuff outside of
update_wall_time().

This allows us to limit the timekeeper_seq hold time to the update of
the real timekeeper and the vsyscall data in the next patch.

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 7ec98e15aa
commit 48cdc135d4
1 changed files with 29 additions and 12 deletions
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41
kernel/time/timekeeping.c
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@ -29,6 +29,7 @@
static struct timekeeper timekeeper;
static DEFINE_RAW_SPINLOCK(timekeeper_lock);
static seqcount_t timekeeper_seq;
static struct timekeeper shadow_timekeeper;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@ -240,7 +241,7 @@ int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
/* must hold timekeeper_lock */
static void timekeeping_update(struct timekeeper *tk, bool clearntp)
static void timekeeping_update(struct timekeeper *tk, bool clearntp, bool mirror)
{
if (clearntp) {
tk->ntp_error = 0;
@ -248,6 +249,9 @@ static void timekeeping_update(struct timekeeper *tk, bool clearntp)
}
update_vsyscall(tk);
update_pvclock_gtod(tk);
if (mirror)
memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
}
/**
@ -504,7 +508,7 @@ int do_settimeofday(const struct timespec *tv)
tk_set_xtime(tk, tv);
timekeeping_update(tk, true);
timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@ -548,7 +552,7 @@ int timekeeping_inject_offset(struct timespec *ts)
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));
error: /* even if we error out, we forwarded the time, so call update */
timekeeping_update(tk, true);
timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@ -628,7 +632,7 @@ static int change_clocksource(void *data)
if (old->disable)
old->disable(old);
}
timekeeping_update(tk, true);
timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@ -809,6 +813,8 @@ void __init timekeeping_init(void)
tmp.tv_nsec = 0;
tk_set_sleep_time(tk, tmp);
memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}
@ -865,7 +871,7 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
__timekeeping_inject_sleeptime(tk, delta);
timekeeping_update(tk, true);
timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@ -947,7 +953,7 @@ static void timekeeping_resume(void)
clock->cycle_last = cycle_now;
tk->ntp_error = 0;
timekeeping_suspended = 0;
timekeeping_update(tk, false);
timekeeping_update(tk, false, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@ -1328,7 +1334,8 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk)
static void update_wall_time(void)
{
struct clocksource *clock;
struct timekeeper *tk = &timekeeper;
struct timekeeper *real_tk = &timekeeper;
struct timekeeper *tk = &shadow_timekeeper;
cycle_t offset;
int shift = 0, maxshift;
unsigned long flags;
@ -1340,16 +1347,16 @@ static void update_wall_time(void)
if (unlikely(timekeeping_suspended))
goto out;
clock = tk->clock;
clock = real_tk->clock;
#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
offset = tk->cycle_interval;
offset = real_tk->cycle_interval;
#else
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif
/* Check if there's really nothing to do */
if (offset < tk->cycle_interval)
if (offset < real_tk->cycle_interval)
goto out;
/*
@ -1388,12 +1395,22 @@ static void update_wall_time(void)
/* Update clock->cycle_last with the new value */
clock->cycle_last = tk->cycle_last;
timekeeping_update(tk, false);
/*
* Update the real timekeeper.
*
* We could avoid this memcpy by switching pointers, but that
* requires changes to all other timekeeper usage sites as
* well, i.e. move the timekeeper pointer getter into the
* spinlocked/seqcount protected sections. And we trade this
* memcpy under the timekeeper_seq against one before we start
* updating.
*/
memcpy(real_tk, tk, sizeof(*tk));
timekeeping_update(real_tk, false, false);
out:
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}
/**