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Commit 6a867a39 authored by John Stultz's avatar John Stultz Committed by Thomas Gleixner
Browse files

time: Remove xtime_cache 



With the earlier logarithmic time accumulation patch, xtime will now
always be within one "tick" of the current time, instead of possibly
half a second off.

This removes the need for the xtime_cache value, which always stored the
time at the last interrupt, so this patch cleans that up removing the
xtime_cache related code.

This patch also addresses an issue with an earlier version of this change,
where xtime_cache was normalizing xtime, which could in some cases be
not valid (ie: tv_nsec == NSEC_PER_SEC). This is fixed by handling
the edge case in update_wall_time().

Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
Cc: Petr Titěra <P.Titera@century.cz>
LKML-Reference: <1270589451-30773-1-git-send-email-johnstul@us.ibm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 9ca7d8e6

include/linux/time.h

+0 −1
Original line number Diff line number Diff line
@@ -150,7 +150,6 @@ extern struct timespec timespec_trunc(struct timespec t, unsigned gran); 
extern int timekeeping_valid_for_hres(void);

extern u64 timekeeping_max_deferment(void);

extern void update_wall_time(void);

extern void update_xtime_cache(u64 nsec);

extern void timekeeping_leap_insert(int leapsecond);



struct tms;

kernel/time/timekeeping.c

+16 −19
Original line number Diff line number Diff line
@@ -165,13 +165,6 @@ struct timespec raw_time; 
/* flag for if timekeeping is suspended */

int __read_mostly timekeeping_suspended;



static struct timespec xtime_cache __attribute__ ((aligned (16)));

void update_xtime_cache(u64 nsec)

{

	xtime_cache = xtime;

	timespec_add_ns(&xtime_cache, nsec);

}



/* must hold xtime_lock */

void timekeeping_leap_insert(int leapsecond)

{
@@ -332,8 +325,6 @@ int do_settimeofday(struct timespec *tv) 


	xtime = *tv;



	update_xtime_cache(0);



	timekeeper.ntp_error = 0;

	ntp_clear();
@@ -559,7 +550,6 @@ void __init timekeeping_init(void) 
	}

	set_normalized_timespec(&wall_to_monotonic,

				-boot.tv_sec, -boot.tv_nsec);

	update_xtime_cache(0);

	total_sleep_time.tv_sec = 0;

	total_sleep_time.tv_nsec = 0;

	write_sequnlock_irqrestore(&xtime_lock, flags);
@@ -593,7 +583,6 @@ static int timekeeping_resume(struct sys_device *dev) 
		wall_to_monotonic = timespec_sub(wall_to_monotonic, ts);

		total_sleep_time = timespec_add_safe(total_sleep_time, ts);

	}

	update_xtime_cache(0);

	/* re-base the last cycle value */

	timekeeper.clock->cycle_last = timekeeper.clock->read(timekeeper.clock);

	timekeeper.ntp_error = 0;
@@ -788,7 +777,6 @@ void update_wall_time(void) 
{

	struct clocksource *clock;

	cycle_t offset;

	u64 nsecs;

	int shift = 0, maxshift;



	/* Make sure we're fully resumed: */
@@ -846,7 +834,9 @@ void update_wall_time(void) 
		timekeeper.ntp_error += neg << timekeeper.ntp_error_shift;

	}



	/* store full nanoseconds into xtime after rounding it up and



	/*

	 * Store full nanoseconds into xtime after rounding it up and

	 * add the remainder to the error difference.

	 */

	xtime.tv_nsec =	((s64) timekeeper.xtime_nsec >> timekeeper.shift) + 1;
@@ -854,8 +844,15 @@ void update_wall_time(void) 
	timekeeper.ntp_error +=	timekeeper.xtime_nsec <<

				timekeeper.ntp_error_shift;



	nsecs = clocksource_cyc2ns(offset, timekeeper.mult, timekeeper.shift);

	update_xtime_cache(nsecs);

	/*

	 * Finally, make sure that after the rounding

	 * xtime.tv_nsec isn't larger then NSEC_PER_SEC

	 */

	if (unlikely(xtime.tv_nsec >= NSEC_PER_SEC)) {

		xtime.tv_nsec -= NSEC_PER_SEC;

		xtime.tv_sec++;

		second_overflow();

	}



	/* check to see if there is a new clocksource to use */

	update_vsyscall(&xtime, timekeeper.clock, timekeeper.mult);
@@ -895,13 +892,13 @@ EXPORT_SYMBOL_GPL(monotonic_to_bootbased); 


unsigned long get_seconds(void)

{

	return xtime_cache.tv_sec;

	return xtime.tv_sec;

}

EXPORT_SYMBOL(get_seconds);



struct timespec __current_kernel_time(void)

{

	return xtime_cache;

	return xtime;

}



struct timespec current_kernel_time(void)
@@ -912,7 +909,7 @@ struct timespec current_kernel_time(void) 
	do {

		seq = read_seqbegin(&xtime_lock);



		now = xtime_cache;

		now = xtime;

	} while (read_seqretry(&xtime_lock, seq));



	return now;
@@ -927,7 +924,7 @@ struct timespec get_monotonic_coarse(void) 
	do {

		seq = read_seqbegin(&xtime_lock);



		now = xtime_cache;

		now = xtime;

		mono = wall_to_monotonic;

	} while (read_seqretry(&xtime_lock, seq));