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-rw-r--r--kernel/timer.c85
1 files changed, 47 insertions, 38 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 396a3c024c2..2a87430a58d 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -891,6 +891,7 @@ int do_settimeofday(struct timespec *tv)
set_normalized_timespec(&xtime, sec, nsec);
set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
+ clock->error = 0;
ntp_clear();
write_sequnlock_irqrestore(&xtime_lock, flags);
@@ -1008,52 +1009,52 @@ static int __init timekeeping_init_device(void)
device_initcall(timekeeping_init_device);
/*
- * If the error is already larger, we look ahead another tick,
+ * If the error is already larger, we look ahead even further
* to compensate for late or lost adjustments.
*/
-static __always_inline int clocksource_bigadjust(int sign, s64 error, s64 *interval, s64 *offset)
+static __always_inline int clocksource_bigadjust(s64 error, s64 *interval, s64 *offset)
{
- int adj;
+ s64 tick_error, i;
+ u32 look_ahead, adj;
+ s32 error2, mult;
/*
- * As soon as the machine is synchronized to the external time
- * source this should be the common case.
+ * Use the current error value to determine how much to look ahead.
+ * The larger the error the slower we adjust for it to avoid problems
+ * with losing too many ticks, otherwise we would overadjust and
+ * produce an even larger error. The smaller the adjustment the
+ * faster we try to adjust for it, as lost ticks can do less harm
+ * here. This is tuned so that an error of about 1 msec is adusted
+ * within about 1 sec (or 2^20 nsec in 2^SHIFT_HZ ticks).
*/
- error >>= 2;
- if (likely(sign > 0 ? error <= *interval : error >= *interval))
- return sign;
+ error2 = clock->error >> (TICK_LENGTH_SHIFT + 22 - 2 * SHIFT_HZ);
+ error2 = abs(error2);
+ for (look_ahead = 0; error2 > 0; look_ahead++)
+ error2 >>= 2;
/*
- * An extra look ahead dampens the effect of the current error,
- * which can grow quite large with continously late updates, as
- * it would dominate the adjustment value and can lead to
- * oscillation.
+ * Now calculate the error in (1 << look_ahead) ticks, but first
+ * remove the single look ahead already included in the error.
*/
- error += current_tick_length() >> (TICK_LENGTH_SHIFT - clock->shift + 1);
- error -= clock->xtime_interval >> 1;
-
- adj = 0;
- while (1) {
- error >>= 1;
- if (sign > 0 ? error <= *interval : error >= *interval)
- break;
- adj++;
+ tick_error = current_tick_length() >> (TICK_LENGTH_SHIFT - clock->shift + 1);
+ tick_error -= clock->xtime_interval >> 1;
+ error = ((error - tick_error) >> look_ahead) + tick_error;
+
+ /* Finally calculate the adjustment shift value. */
+ i = *interval;
+ mult = 1;
+ if (error < 0) {
+ error = -error;
+ *interval = -*interval;
+ *offset = -*offset;
+ mult = -1;
}
-
- /*
- * Add the current adjustments to the error and take the offset
- * into account, the latter can cause the error to be hardly
- * reduced at the next tick. Check the error again if there's
- * room for another adjustment, thus further reducing the error
- * which otherwise had to be corrected at the next update.
- */
- error = (error << 1) - *interval + *offset;
- if (sign > 0 ? error > *interval : error < *interval)
- adj++;
+ for (adj = 0; error > i; adj++)
+ error >>= 1;
*interval <<= adj;
*offset <<= adj;
- return sign << adj;
+ return mult << adj;
}
/*
@@ -1068,11 +1069,19 @@ static void clocksource_adjust(struct clocksource *clock, s64 offset)
error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1);
if (error > interval) {
- adj = clocksource_bigadjust(1, error, &interval, &offset);
+ error >>= 2;
+ if (likely(error <= interval))
+ adj = 1;
+ else
+ adj = clocksource_bigadjust(error, &interval, &offset);
} else if (error < -interval) {
- interval = -interval;
- offset = -offset;
- adj = clocksource_bigadjust(-1, error, &interval, &offset);
+ error >>= 2;
+ if (likely(error >= -interval)) {
+ adj = -1;
+ interval = -interval;
+ offset = -offset;
+ } else
+ adj = clocksource_bigadjust(error, &interval, &offset);
} else
return;
@@ -1129,7 +1138,7 @@ static void update_wall_time(void)
clocksource_adjust(clock, offset);
/* store full nanoseconds into xtime */
- xtime.tv_nsec = clock->xtime_nsec >> clock->shift;
+ xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
/* check to see if there is a new clocksource to use */