[PATCH] fix and optimize clock source update

This fixes the clock source updates in update_wall_time() to correctly
track the time coming in via current_tick_length().  Optimize the fast
paths to be as short as possible to keep the overhead low.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Acked-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 12 insertions, 105 deletions

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 4bc94282c36..d852024ed09 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -46,8 +46,8 @@ typedef u64 cycle_t;
  * @shift:		cycle to nanosecond divisor (power of two)
  * @update_callback:	called when safe to alter clocksource values
  * @is_continuous:	defines if clocksource is free-running.
- * @interval_cycles:	Used internally by timekeeping core, please ignore.
- * @interval_snsecs:	Used internally by timekeeping core, please ignore.
+ * @cycle_interval:	Used internally by timekeeping core, please ignore.
+ * @xtime_interval:	Used internally by timekeeping core, please ignore.
  */
 struct clocksource {
 	char *name;
@@ -61,8 +61,9 @@ struct clocksource {
 	int is_continuous;
 
 	/* timekeeping specific data, ignore */
-	cycle_t interval_cycles;
-	u64 interval_snsecs;
+	cycle_t cycle_last, cycle_interval;
+	u64 xtime_nsec, xtime_interval;
+	s64 error;
 };
 
 /* simplify initialization of mask field */
@@ -168,107 +169,11 @@ static inline void clocksource_calculate_interval(struct clocksource *c,
 	tmp += c->mult/2;
 	do_div(tmp, c->mult);
 
-	c->interval_cycles = (cycle_t)tmp;
-	if(c->interval_cycles == 0)
-		c->interval_cycles = 1;
+	c->cycle_interval = (cycle_t)tmp;
+	if (c->cycle_interval == 0)
+		c->cycle_interval = 1;
 
-	c->interval_snsecs = (u64)c->interval_cycles * c->mult;
-}
-
-
-/**
- * error_aproximation - calculates an error adjustment for a given error
- *
- * @error:	Error value (unsigned)
- * @unit:	Adjustment unit
- *
- * For a given error value, this function takes the adjustment unit
- * and uses binary approximation to return a power of two adjustment value.
- *
- * This function is only for use by the the make_ntp_adj() function
- * and you must hold a write on the xtime_lock when calling.
- */
-static inline int error_aproximation(u64 error, u64 unit)
-{
-	static int saved_adj = 0;
-	u64 adjusted_unit = unit << saved_adj;
-
-	if (error > (adjusted_unit * 2)) {
-		/* large error, so increment the adjustment factor */
-		saved_adj++;
-	} else if (error > adjusted_unit) {
-		/* just right, don't touch it */
-	} else if (saved_adj) {
-		/* small error, so drop the adjustment factor */
-		saved_adj--;
-		return 0;
-	}
-
-	return saved_adj;
-}
-
-
-/**
- * make_ntp_adj - Adjusts the specified clocksource for a given error
- *
- * @clock:		Pointer to clock to be adjusted
- * @cycles_delta:	Current unacounted cycle delta
- * @error:		Pointer to current error value
- *
- * Returns clock shifted nanosecond adjustment to be applied against
- * the accumulated time value (ie: xtime).
- *
- * If the error value is large enough, this function calulates the
- * (power of two) adjustment value, and adjusts the clock's mult and
- * interval_snsecs values accordingly.
- *
- * However, since there may be some unaccumulated cycles, to avoid
- * time inconsistencies we must adjust the accumulation value
- * accordingly.
- *
- * This is not very intuitive, so the following proof should help:
- * The basic timeofday algorithm:  base + cycle * mult
- * Thus:
- *    new_base + cycle * new_mult = old_base + cycle * old_mult
- *    new_base = old_base + cycle * old_mult - cycle * new_mult
- *    new_base = old_base + cycle * (old_mult - new_mult)
- *    new_base - old_base = cycle * (old_mult - new_mult)
- *    base_delta = cycle * (old_mult - new_mult)
- *    base_delta = cycle * (mult_delta)
- *
- * Where mult_delta is the adjustment value made to mult
- *
- */
-static inline s64 make_ntp_adj(struct clocksource *clock,
-				cycles_t cycles_delta, s64* error)
-{
-	s64 ret = 0;
-	if (*error  > ((s64)clock->interval_cycles+1)/2) {
-		/* calculate adjustment value */
-		int adjustment = error_aproximation(*error,
-						clock->interval_cycles);
-		/* adjust clock */
-		clock->mult += 1 << adjustment;
-		clock->interval_snsecs += clock->interval_cycles << adjustment;
-
-		/* adjust the base and error for the adjustment */
-		ret =  -(cycles_delta << adjustment);
-		*error -= clock->interval_cycles << adjustment;
-		/* XXX adj error for cycle_delta offset? */
-	} else if ((-(*error))  > ((s64)clock->interval_cycles+1)/2) {
-		/* calculate adjustment value */
-		int adjustment = error_aproximation(-(*error),
-						clock->interval_cycles);
-		/* adjust clock */
-		clock->mult -= 1 << adjustment;
-		clock->interval_snsecs -= clock->interval_cycles << adjustment;
-
-		/* adjust the base and error for the adjustment */
-		ret =  cycles_delta << adjustment;
-		*error += clock->interval_cycles << adjustment;
-		/* XXX adj error for cycle_delta offset? */
-	}
-	return ret;
+	c->xtime_interval = (u64)c->cycle_interval * c->mult;
 }
 
 
diff --git a/include/linux/timex.h b/include/linux/timex.h
index 1ba3071fcb8..19bb6538b49 100644
--- a/include/linux/timex.h
+++ b/include/linux/timex.h
@@ -303,8 +303,10 @@ time_interpolator_reset(void)
 
 #endif /* !CONFIG_TIME_INTERPOLATION */
 
+#define TICK_LENGTH_SHIFT	32
+
 /* Returns how long ticks are at present, in ns / 2^(SHIFT_SCALE-10). */
-extern u64 current_tick_length(long);
+extern u64 current_tick_length(void);
 
 extern int do_adjtimex(struct timex *);