[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>
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 4bc9428..d852024 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -46,8 +46,8 @@
* @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 @@
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 @@
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;
}