time: Remove xtime_cache

With the prior 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 is a bit simpler, but still could use some wider testing.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: John Kacur <jkacur@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <1254525855.7741.95.camel@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Cherry-picked from timers/core. Conflicts:

	kernel/time.c
	kernel/time/timekeeping.c
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/time.c

@@ -136,7 +136,6 @@ static inline void warp_clock(void)
 	write_atomic_seqlock_irq(&xtime_lock);
 	wall_to_monotonic.tv_sec -= sys_tz.tz_minuteswest * 60;
 	xtime.tv_sec += sys_tz.tz_minuteswest * 60;
-	update_xtime_cache(0);
 	write_atomic_sequnlock_irq(&xtime_lock);
 	clock_was_set();
 }

kernel/time/timekeeping.c

@@ -48,16 +48,8 @@ static unsigned long total_sleep_time;		/* seconds */
 /* 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);
-}
-
 struct clocksource *clock;
 
-
 #ifdef CONFIG_GENERIC_TIME
 /**
  * clocksource_forward_now - update clock to the current time
@@ -233,8 +225,6 @@ int do_settimeofday(struct timespec *tv)
 
 	xtime = *tv;
 
-	update_xtime_cache(0);
-
 	clock->error = 0;
 	ntp_clear();
 
@@ -435,7 +425,6 @@ void __init timekeeping_init(void)
 	xtime.tv_nsec = 0;
 	set_normalized_timespec(&wall_to_monotonic,
 				-xtime.tv_sec, -xtime.tv_nsec);
-	update_xtime_cache(0);
 	total_sleep_time = 0;
 	write_atomic_sequnlock_irqrestore(&xtime_lock, flags);
 }
@@ -467,7 +456,6 @@ static int timekeeping_resume(struct sys_device *dev)
 		wall_to_monotonic.tv_sec -= sleep_length;
 		total_sleep_time += sleep_length;
 	}
-	update_xtime_cache(0);
 	/* re-base the last cycle value */
 	clock->cycle_last = 0;
 	clock->cycle_last = clocksource_read(clock);
@@ -608,7 +596,6 @@ static void clocksource_adjust(s64 offset)
 			(NTP_SCALE_SHIFT - clock->shift);
 }
 
-
 /**
  * logarithmic_accumulation - shifted accumulation of cycles
  *
@@ -652,7 +639,6 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
 	return offset;
 }
 
-
 /**
  * update_wall_time - Uses the current clocksource to increment the wall time
  *
@@ -724,8 +710,6 @@ void update_wall_time(void)
 	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 	clock->error += clock->xtime_nsec << (NTP_SCALE_SHIFT - clock->shift);
 
-	update_xtime_cache(cyc2ns(clock, offset));
-
 	/* check to see if there is a new clocksource to use */
 	change_clocksource();
 	update_vsyscall(&xtime, clock);
@@ -760,11 +744,10 @@ void monotonic_to_bootbased(struct timespec *ts)
 
 unsigned long get_seconds(void)
 {
-	return xtime_cache.tv_sec;
+	return xtime.tv_sec;
 }
 EXPORT_SYMBOL(get_seconds);
 
-
 struct timespec current_kernel_time(void)
 {
 	struct timespec now;
@@ -772,10 +755,10 @@ struct timespec current_kernel_time(void)
 
 	do {
 		seq = read_atomic_seqbegin(&xtime_lock);
-
-		now = xtime_cache;
+		now = xtime;
 	} while (read_atomic_seqretry(&xtime_lock, seq));
 
 	return now;
 }
 EXPORT_SYMBOL(current_kernel_time);
+