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Commit 48cdc135 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by John Stultz
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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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 7ec98e15

kernel/time/timekeeping.c

+29 −12
Original line number Diff line number Diff line
@@ -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);



}



/**