timer: Reduce timers softirq v3

index 9a838d38dbe6..df1ff803acc4 100644
@@ -521,8 +521,8 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk)
 		 * Force expire obscene large timeouts to expire at the
 		 * capacity limit of the wheel.
 		 */
-		if (expires >= WHEEL_TIMEOUT_CUTOFF)
-			expires = WHEEL_TIMEOUT_MAX;
+		if (delta >= WHEEL_TIMEOUT_CUTOFF)
+			expires = clk + WHEEL_TIMEOUT_MAX;
 
 		idx = calc_index(expires, LVL_DEPTH - 1);
 	}

index df1ff803acc4..bcdc3045138d 100644
@@ -487,7 +487,7 @@ static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
  * Helper function to calculate the array index for a given expiry
  * time.
  */
-static inline unsigned calc_index(unsigned expires, unsigned lvl)
+static inline unsigned calc_index(unsigned long expires, unsigned lvl)
 {
 	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
 	return LVL_OFFS(lvl) + (expires & LVL_MASK);

index bcdc3045138d..a7a3cf737411 100644
@@ -487,35 +487,39 @@ static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
  * Helper function to calculate the array index for a given expiry
  * time.
  */
-static inline unsigned calc_index(unsigned long expires, unsigned lvl)
+static inline unsigned calc_index(unsigned long expires, unsigned lvl,
+				  unsigned long *bucket_expiry)
 {
 	expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl);
+	*bucket_expiry = expires << LVL_SHIFT(lvl);
 	return LVL_OFFS(lvl) + (expires & LVL_MASK);
 }
 
-static int calc_wheel_index(unsigned long expires, unsigned long clk)
+static int calc_wheel_index(unsigned long expires, unsigned long clk,
+			    unsigned long *bucket_expiry)
 {
 	unsigned long delta = expires - clk;
 	unsigned int idx;
 
 	if (delta < LVL_START(1)) {
-		idx = calc_index(expires, 0);
+		idx = calc_index(expires, 0, bucket_expiry);
 	} else if (delta < LVL_START(2)) {
-		idx = calc_index(expires, 1);
+		idx = calc_index(expires, 1, bucket_expiry);
 	} else if (delta < LVL_START(3)) {
-		idx = calc_index(expires, 2);
+		idx = calc_index(expires, 2, bucket_expiry);
 	} else if (delta < LVL_START(4)) {
-		idx = calc_index(expires, 3);
+		idx = calc_index(expires, 3, bucket_expiry);
 	} else if (delta < LVL_START(5)) {
-		idx = calc_index(expires, 4);
+		idx = calc_index(expires, 4, bucket_expiry);
 	} else if (delta < LVL_START(6)) {
-		idx = calc_index(expires, 5);
+		idx = calc_index(expires, 5, bucket_expiry);
 	} else if (delta < LVL_START(7)) {
-		idx = calc_index(expires, 6);
+		idx = calc_index(expires, 6, bucket_expiry);
 	} else if (LVL_DEPTH > 8 && delta < LVL_START(8)) {
-		idx = calc_index(expires, 7);
+		idx = calc_index(expires, 7, bucket_expiry);
 	} else if ((long) delta < 0) {
 		idx = clk & LVL_MASK;
+		*bucket_expiry = clk;
 	} else {
 		/*
 		 * Force expire obscene large timeouts to expire at the

@@ -524,7 +528,7 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk)
 		if (delta >= WHEEL_TIMEOUT_CUTOFF)
 			expires = clk + WHEEL_TIMEOUT_MAX;
 
-		idx = calc_index(expires, LVL_DEPTH - 1);
+		idx = calc_index(expires, LVL_DEPTH - 1, bucket_expiry);
 	}
 	return idx;
 }

@@ -544,16 +548,18 @@ static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
 }
 
 static void
-__internal_add_timer(struct timer_base *base, struct timer_list *timer)
+__internal_add_timer(struct timer_base *base, struct timer_list *timer,
+		     unsigned long *bucket_expiry)
 {
 	unsigned int idx;
 
-	idx = calc_wheel_index(timer->expires, base->clk);
+	idx = calc_wheel_index(timer->expires, base->clk, bucket_expiry);
 	enqueue_timer(base, timer, idx);
 }
 
 static void
-trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
+trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
+		    unsigned long bucket_expiry)
 {
 	if (!is_timers_nohz_active())
 		return;

@@ -576,31 +582,29 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 	if (!base->is_idle)
 		return;
 
-	/* Check whether this is the new first expiring timer: */
-	if (time_after_eq(timer->expires, base->next_expiry))
+	/*
+	 * Check whether this is the new first expiring timer. The
+	 * effective expiry time of the timer is required here
+	 * (bucket_expiry) instead of timer->expires.
+	 */
+	if (time_after_eq(bucket_expiry, base->next_expiry))
 		return;
 
 	/*
 	 * Set the next expiry time and kick the CPU so it can reevaluate the
 	 * wheel:
 	 */
-	if (time_before(timer->expires, base->clk)) {
-		/*
-		 * Prevent from forward_timer_base() moving the base->clk
-		 * backward
-		 */
-		base->next_expiry = base->clk;
-	} else {
-		base->next_expiry = timer->expires;
-	}
+	base->next_expiry = bucket_expiry;
 	wake_up_nohz_cpu(base->cpu);
 }
 
 static void
 internal_add_timer(struct timer_base *base, struct timer_list *timer)
 {
-	__internal_add_timer(base, timer);
-	trigger_dyntick_cpu(base, timer);
+	unsigned long bucket_expiry;
+
+	__internal_add_timer(base, timer, &bucket_expiry);
+	trigger_dyntick_cpu(base, timer, bucket_expiry);
 }
 
 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS

@@ -959,9 +963,9 @@ static struct timer_base *lock_timer_base(struct timer_list *timer,
 static inline int
 __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int options)
 {
+	unsigned long clk = 0, flags, bucket_expiry;
 	struct timer_base *base, *new_base;
 	unsigned int idx = UINT_MAX;
-	unsigned long clk = 0, flags;
 	int ret = 0;
 
 	BUG_ON(!timer->function);

@@ -1000,7 +1004,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option
 		}
 
 		clk = base->clk;
-		idx = calc_wheel_index(expires, clk);
+		idx = calc_wheel_index(expires, clk, &bucket_expiry);
 
 		/*
 		 * Retrieve and compare the array index of the pending

@@ -1059,7 +1063,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option
 	 */
 	if (idx != UINT_MAX && clk == base->clk) {
 		enqueue_timer(base, timer, idx);
-		trigger_dyntick_cpu(base, timer);
+		trigger_dyntick_cpu(base, timer, bucket_expiry);
 	} else {
 		internal_add_timer(base, timer);
 	}

index a7a3cf737411..2af08a169564 100644
@@ -533,30 +533,6 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk,
 	return idx;
 }
 
-/*
- * Enqueue the timer into the hash bucket, mark it pending in
- * the bitmap and store the index in the timer flags.
- */
-static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
-			  unsigned int idx)
-{
-	hlist_add_head(&timer->entry, base->vectors + idx);
-	__set_bit(idx, base->pending_map);
-	timer_set_idx(timer, idx);
-
-	trace_timer_start(timer, timer->expires, timer->flags);
-}
-
-static void
-__internal_add_timer(struct timer_base *base, struct timer_list *timer,
-		     unsigned long *bucket_expiry)
-{
-	unsigned int idx;
-
-	idx = calc_wheel_index(timer->expires, base->clk, bucket_expiry);
-	enqueue_timer(base, timer, idx);
-}
-
 static void
 trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
 		    unsigned long bucket_expiry)

@@ -598,15 +574,31 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
 	wake_up_nohz_cpu(base->cpu);
 }
 
-static void
-internal_add_timer(struct timer_base *base, struct timer_list *timer)
+/*
+ * Enqueue the timer into the hash bucket, mark it pending in
+ * the bitmap, store the index in the timer flags then wake up
+ * the target CPU if needed.
+ */
+static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
+			  unsigned int idx, unsigned long bucket_expiry)
 {
-	unsigned long bucket_expiry;
+	hlist_add_head(&timer->entry, base->vectors + idx);
+	__set_bit(idx, base->pending_map);
+	timer_set_idx(timer, idx);
 
-	__internal_add_timer(base, timer, &bucket_expiry);
+	trace_timer_start(timer, timer->expires, timer->flags);
 	trigger_dyntick_cpu(base, timer, bucket_expiry);
 }
 
+static void internal_add_timer(struct timer_base *base, struct timer_list *timer)
+{
+	unsigned long bucket_expiry;
+	unsigned int idx;
+
+	idx = calc_wheel_index(timer->expires, base->clk, &bucket_expiry);
+	enqueue_timer(base, timer, idx, bucket_expiry);
+}
+
 #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
 
 static struct debug_obj_descr timer_debug_descr;

@@ -1057,16 +1049,13 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option
 	/*
 	 * If 'idx' was calculated above and the base time did not advance
 	 * between calculating 'idx' and possibly switching the base, only
-	 * enqueue_timer() and trigger_dyntick_cpu() is required. Otherwise
-	 * we need to (re)calculate the wheel index via
-	 * internal_add_timer().
+	 * enqueue_timer() is required. Otherwise we need to (re)calculate
+	 * the wheel index via internal_add_timer().
 	 */
-	if (idx != UINT_MAX && clk == base->clk) {
-		enqueue_timer(base, timer, idx);
-		trigger_dyntick_cpu(base, timer, bucket_expiry);
-	} else {
+	if (idx != UINT_MAX && clk == base->clk)
+		enqueue_timer(base, timer, idx, bucket_expiry);
+	else
 		internal_add_timer(base, timer);
-	}
 
 out_unlock:
 	raw_spin_unlock_irqrestore(&base->lock, flags);

index 2af08a169564..af1c08b0b168 100644
@@ -156,7 +156,8 @@ EXPORT_SYMBOL(jiffies_64);
 
 /*
  * 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))
 

@@ -490,6 +491,15 @@ static inline void timer_set_idx(struct timer_list *timer, unsigned int idx)
 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);

index af1c08b0b168..9abc41715fd2 100644
@@ -1526,6 +1526,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base)
 	clk = base->clk;
 	for (lvl = 0; lvl < LVL_DEPTH; lvl++, offset += LVL_SIZE) {
 		int pos = next_pending_bucket(base, offset, clk & LVL_MASK);
+		unsigned long lvl_clk = clk & LVL_CLK_MASK;
 
 		if (pos >= 0) {
 			unsigned long tmp = clk + (unsigned long) pos;

@@ -1533,6 +1534,13 @@ static unsigned long __next_timer_interrupt(struct timer_base *base)
 			tmp <<= LVL_SHIFT(lvl);
 			if (time_before(tmp, next))
 				next = tmp;
+
+			/*
+			 * If the next expiration happens before we reach
+			 * the next level, no need to check further.
+			 */
+			if (pos <= ((LVL_CLK_DIV - lvl_clk) & LVL_CLK_MASK))
+				break;
 		}
 		/*
 		 * Clock for the next level. If the current level clock lower

@@ -1570,7 +1578,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base)
 		 * So the simple check whether the lower bits of the current
 		 * level are 0 or not is sufficient for all cases.
 		 */
-		adj = clk & LVL_CLK_MASK ? 1 : 0;
+		adj = lvl_clk ? 1 : 0;
 		clk >>= LVL_CLK_SHIFT;
 		clk += adj;
 	}

index 9abc41715fd2..76fd9644638b 100644
@@ -544,8 +544,7 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk,
 }
 
 static void
-trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
-		    unsigned long bucket_expiry)
+trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 {
 	if (!is_timers_nohz_active())
 		return;

@@ -565,23 +564,8 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
 	 * timer is not deferrable. If the other CPU is on the way to idle
 	 * then it can't set base->is_idle as we hold the base lock:
 	 */
-	if (!base->is_idle)
-		return;
-
-	/*
-	 * Check whether this is the new first expiring timer. The
-	 * effective expiry time of the timer is required here
-	 * (bucket_expiry) instead of timer->expires.
-	 */
-	if (time_after_eq(bucket_expiry, base->next_expiry))
-		return;
-
-	/*
-	 * Set the next expiry time and kick the CPU so it can reevaluate the
-	 * wheel:
-	 */
-	base->next_expiry = bucket_expiry;
-	wake_up_nohz_cpu(base->cpu);
+	if (base->is_idle)
+		wake_up_nohz_cpu(base->cpu);
 }
 
 /*

@@ -592,12 +576,26 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer,
 static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
 			  unsigned int idx, unsigned long bucket_expiry)
 {
+
 	hlist_add_head(&timer->entry, base->vectors + idx);
 	__set_bit(idx, base->pending_map);
 	timer_set_idx(timer, idx);
 
 	trace_timer_start(timer, timer->expires, timer->flags);
-	trigger_dyntick_cpu(base, timer, bucket_expiry);
+
+	/*
+	 * Check whether this is the new first expiring timer. The
+	 * effective expiry time of the timer is required here
+	 * (bucket_expiry) instead of timer->expires.
+	 */
+	if (time_before(bucket_expiry, base->next_expiry)) {
+		/*
+		 * Set the next expiry time and kick the CPU so it
+		 * can reevaluate the wheel:
+		 */
+		base->next_expiry = bucket_expiry;
+		trigger_dyntick_cpu(base, timer);
+	}
 }
 
 static void internal_add_timer(struct timer_base *base, struct timer_list *timer)

@@ -1493,7 +1491,6 @@ static int __collect_expired_timers(struct timer_base *base,
 	return levels;
 }
 
-#ifdef CONFIG_NO_HZ_COMMON
 /*
  * Find the next pending bucket of a level. Search from level start (@offset)
  * + @clk upwards and if nothing there, search from start of the level

@@ -1585,6 +1582,7 @@ static unsigned long __next_timer_interrupt(struct timer_base *base)
 	return next;
 }
 
+#ifdef CONFIG_NO_HZ_COMMON
 /*
  * Check, if the next hrtimer event is before the next timer wheel
  * event:

@@ -1790,6 +1788,7 @@ static inline void __run_timers(struct timer_base *base)
 
 		levels = collect_expired_timers(base, heads);
 		base->clk++;
+		base->next_expiry = __next_timer_interrupt(base);
 
 		while (levels--)
 			expire_timers(base, heads + levels);

@@ -2042,6 +2041,7 @@ static void __init init_timer_cpu(int cpu)
 		base->cpu = cpu;
 		raw_spin_lock_init(&base->lock);
 		base->clk = jiffies;
+		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
 		timer_base_init_expiry_lock(base);
 	}
 }

index 76fd9644638b..13f48ee708aa 100644
@@ -1706,13 +1706,11 @@ static int collect_expired_timers(struct timer_base *base,
 	 * the next expiring timer.
 	 */
 	if ((long)(now - base->clk) > 2) {
-		unsigned long next = __next_timer_interrupt(base);
-
 		/*
 		 * If the next timer is ahead of time forward to current
 		 * jiffies, otherwise forward to the next expiry time:
 		 */
-		if (time_after(next, now)) {
+		if (time_after(base->next_expiry, now)) {
 			/*
 			 * The call site will increment base->clk and then
 			 * terminate the expiry loop immediately.

@@ -1720,7 +1718,7 @@ static int collect_expired_timers(struct timer_base *base,
 			base->clk = now;
 			return 0;
 		}
-		base->clk = next;
+		base->clk = base->next_expiry;
 	}
 	return __collect_expired_timers(base, heads);
 }

index 13f48ee708aa..1be92b53b75f 100644
@@ -888,19 +888,12 @@ get_target_base(struct timer_base *base, unsigned tflags)
 
 static inline void forward_timer_base(struct timer_base *base)
 {
-#ifdef CONFIG_NO_HZ_COMMON
 	unsigned long jnow;
 
-	/*
-	 * We only forward the base when we are idle or have just come out of
-	 * idle (must_forward_clk logic), and have a delta between base clock
-	 * and jiffies. In the common case, run_timers will take care of it.
-	 */
-	if (likely(!base->must_forward_clk))
+	if (!base->must_forward_clk)
 		return;
 
 	jnow = READ_ONCE(jiffies);
-	base->must_forward_clk = base->is_idle;
 	if ((long)(jnow - base->clk) < 2)
 		return;
 

@@ -915,7 +908,6 @@ static inline void forward_timer_base(struct timer_base *base)
 			return;
 		base->clk = base->next_expiry;
 	}
-#endif
 }
 
 

@@ -1667,10 +1659,8 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
 		 * logic is only maintained for the BASE_STD base, deferrable
 		 * timers may still see large granularity skew (by design).
 		 */
-		if ((expires - basem) > TICK_NSEC) {
-			base->must_forward_clk = true;
+		if ((expires - basem) > TICK_NSEC)
 			base->is_idle = true;
-		}
 	}
 	raw_spin_unlock(&base->lock);
 

@@ -1769,16 +1759,7 @@ static inline void __run_timers(struct timer_base *base)
 	/*
 	 * timer_base::must_forward_clk must be cleared before running
 	 * timers so that any timer functions that call mod_timer() will
-	 * not try to forward the base. Idle tracking / clock forwarding
-	 * logic is only used with BASE_STD timers.
-	 *
-	 * The must_forward_clk flag is cleared unconditionally also for
-	 * the deferrable base. The deferrable base is not affected by idle
-	 * tracking and never forwarded, so clearing the flag is a NOOP.
-	 *
-	 * The fact that the deferrable base is never forwarded can cause
-	 * large variations in granularity for deferrable timers, but they
-	 * can be deferred for long periods due to idle anyway.
+	 * not try to forward the base.
 	 */
 	base->must_forward_clk = false;
 

@@ -1791,6 +1772,7 @@ static inline void __run_timers(struct timer_base *base)
 		while (levels--)
 			expire_timers(base, heads + levels);
 	}
+	base->must_forward_clk = true;
 	raw_spin_unlock_irq(&base->lock);
 	timer_base_unlock_expiry(base);
 }

index 1be92b53b75f..4f78a7bff9e1 100644
@@ -1458,10 +1458,10 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
 	}
 }
 
-static int __collect_expired_timers(struct timer_base *base,
-				    struct hlist_head *heads)
+static int collect_expired_timers(struct timer_base *base,
+				  struct hlist_head *heads)
 {
-	unsigned long clk = base->clk;
+	unsigned long clk = base->clk = base->next_expiry;
 	struct hlist_head *vec;
 	int i, levels = 0;
 	unsigned int idx;

@@ -1684,40 +1684,6 @@ void timer_clear_idle(void)
 	 */
 	base->is_idle = false;
 }
-
-static int collect_expired_timers(struct timer_base *base,
-				  struct hlist_head *heads)
-{
-	unsigned long now = READ_ONCE(jiffies);
-
-	/*
-	 * NOHZ optimization. After a long idle sleep we need to forward the
-	 * base to current jiffies. Avoid a loop by searching the bitfield for
-	 * the next expiring timer.
-	 */
-	if ((long)(now - base->clk) > 2) {
-		/*
-		 * If the next timer is ahead of time forward to current
-		 * jiffies, otherwise forward to the next expiry time:
-		 */
-		if (time_after(base->next_expiry, now)) {
-			/*
-			 * The call site will increment base->clk and then
-			 * terminate the expiry loop immediately.
-			 */
-			base->clk = now;
-			return 0;
-		}
-		base->clk = base->next_expiry;
-	}
-	return __collect_expired_timers(base, heads);
-}
-#else
-static inline int collect_expired_timers(struct timer_base *base,
-					 struct hlist_head *heads)
-{
-	return __collect_expired_timers(base, heads);
-}
 #endif
 
 /*

@@ -1750,7 +1716,7 @@ static inline void __run_timers(struct timer_base *base)
 	struct hlist_head heads[LVL_DEPTH];
 	int levels;
 
-	if (!time_after_eq(jiffies, base->clk))
+	if (time_before(jiffies, base->next_expiry))
 		return;
 
 	timer_base_lock_expiry(base);

@@ -1763,7 +1729,8 @@ static inline void __run_timers(struct timer_base *base)
 	 */
 	base->must_forward_clk = false;
 
-	while (time_after_eq(jiffies, base->clk)) {
+	while (time_after_eq(jiffies, base->clk) &&
+	       time_after_eq(jiffies, base->next_expiry)) {
 
 		levels = collect_expired_timers(base, heads);
 		base->clk++;

@@ -1798,12 +1765,12 @@ void run_local_timers(void)
 
 	hrtimer_run_queues();
 	/* Raise the softirq only if required. */
-	if (time_before(jiffies, base->clk)) {
+	if (time_before(jiffies, base->next_expiry)) {
 		if (!IS_ENABLED(CONFIG_NO_HZ_COMMON))
 			return;
 		/* CPU is awake, so check the deferrable base. */
 		base++;
-		if (time_before(jiffies, base->clk))
+		if (time_before(jiffies, base->next_expiry))
 			return;
 	}
 	raise_softirq(TIMER_SOFTIRQ);

index 4f78a7bff9e1..8b3fb52d8c47 100644
@@ -205,7 +205,6 @@ struct timer_base {
 	unsigned long		next_expiry;
 	unsigned int		cpu;
 	bool			is_idle;
-	bool			must_forward_clk;
 	DECLARE_BITMAP(pending_map, WHEEL_SIZE);
 	struct hlist_head	vectors[WHEEL_SIZE];
 } ____cacheline_aligned;

@@ -888,12 +887,13 @@ get_target_base(struct timer_base *base, unsigned tflags)
 
 static inline void forward_timer_base(struct timer_base *base)
 {
-	unsigned long jnow;
+	unsigned long jnow = READ_ONCE(jiffies);
 
-	if (!base->must_forward_clk)
-		return;
-
-	jnow = READ_ONCE(jiffies);
+	/*
+	 * No need to forward if we are close enough below jiffies.
+	 * Also while executing timers, base->clk is 1 offset ahead
+	 * of jiffies to avoid endless requeuing to current jffies.
+	 */
 	if ((long)(jnow - base->clk) < 2)
 		return;
 

@@ -1722,16 +1722,8 @@ static inline void __run_timers(struct timer_base *base)
 	timer_base_lock_expiry(base);
 	raw_spin_lock_irq(&base->lock);
 
-	/*
-	 * timer_base::must_forward_clk must be cleared before running
-	 * timers so that any timer functions that call mod_timer() will
-	 * not try to forward the base.
-	 */
-	base->must_forward_clk = false;
-
 	while (time_after_eq(jiffies, base->clk) &&
 	       time_after_eq(jiffies, base->next_expiry)) {
-
 		levels = collect_expired_timers(base, heads);
 		base->clk++;
 		base->next_expiry = __next_timer_interrupt(base);

@@ -1739,7 +1731,6 @@ static inline void __run_timers(struct timer_base *base)
 		while (levels--)
 			expire_timers(base, heads + levels);
 	}
-	base->must_forward_clk = true;
 	raw_spin_unlock_irq(&base->lock);
 	timer_base_unlock_expiry(base);
 }

@@ -1935,7 +1926,6 @@ int timers_prepare_cpu(unsigned int cpu)
 		base->clk = jiffies;
 		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
 		base->is_idle = false;
-		base->must_forward_clk = true;
 	}
 	return 0;
 }

index 8b3fb52d8c47..77e21e98ec32 100644
@@ -894,7 +894,7 @@ static inline void forward_timer_base(struct timer_base *base)
 	 * Also while executing timers, base->clk is 1 offset ahead
 	 * of jiffies to avoid endless requeuing to current jffies.
 	 */
-	if ((long)(jnow - base->clk) < 2)
+	if ((long)(jnow - base->clk) < 1)
 		return;
 
 	/*