/*
* The time start value for each level to select the bucket at enqueue
- * time.
+ * time. We start from the last possible delta of the previous level
+ * so that we can later add an extra LVL_GRAN(n) to n (see calc_index()).
*/
#define LVL_START(n) ((LVL_SIZE - 1) << (((n) - 1) * LVL_CLK_SHIFT))
static inline unsigned calc_index(unsigned long expires, unsigned lvl,
unsigned long *bucket_expiry)
{
+
+ /*
+ * The timer wheel has to guarantee that a timer does not fire
+ * early. Early expiry can happen due to:
+ * - Timer is armed at the edge of a tick
+ * - Truncation of the expiry time in the outer wheel levels
+ *
+ * Round up with level granularity to prevent this.
+ */
expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
*bucket_expiry = expires << LVL_SHIFT(lvl);
return LVL_OFFS(lvl) + (expires & LVL_MASK);