+/*
+ * If the error is already larger, we look ahead another tick,
+ * to compensate for late or lost adjustments.
+ */
+static __always_inline int clocksource_bigadjust(int sign, s64 error, s64 *interval, s64 *offset)
+{
+ int adj;
+
+ /*
+ * As soon as the machine is synchronized to the external time
+ * source this should be the common case.
+ */
+ error >>= 2;
+ if (likely(sign > 0 ? error <= *interval : error >= *interval))
+ return sign;
+
+ /*
+ * 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.
+ */
+ 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++;
+ }
+
+ /*
+ * 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++;
+
+ *interval <<= adj;
+ *offset <<= adj;
+ return sign << adj;
+}
+
+/*
+ * Adjust the multiplier to reduce the error value,
+ * this is optimized for the most common adjustments of -1,0,1,
+ * for other values we can do a bit more work.
+ */
+static void clocksource_adjust(struct clocksource *clock, s64 offset)
+{
+ s64 error, interval = clock->cycle_interval;
+ int adj;
+
+ error = clock->error >> (TICK_LENGTH_SHIFT - clock->shift - 1);
+ if (error > interval) {
+ adj = clocksource_bigadjust(1, error, &interval, &offset);
+ } else if (error < -interval) {
+ interval = -interval;
+ offset = -offset;
+ adj = clocksource_bigadjust(-1, error, &interval, &offset);
+ } else
+ return;
+
+ clock->mult += adj;
+ clock->xtime_interval += interval;
+ clock->xtime_nsec -= offset;
+ clock->error -= (interval - offset) << (TICK_LENGTH_SHIFT - clock->shift);
+}
+