[PATCH 4/9] timers: Always keep track of next expiry

[Frederic Weisbecker]

So far next expiry was only tracked while the CPU was in nohz_idle mode
in order to cope with missing ticks that can't increment the base->clk
periodically anymore.

We are going to expand that logic beyond nohz in order to spare timers
softirqs so do it unconditionally.

Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Anna-Maria Gleixner <anna-maria@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
---
 kernel/time/timer.c | 36 +++++++++++++++++++-----------------
 1 file changed, 19 insertions(+), 17 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index acf7cb8c09f8..8a4138e47aa4 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -558,8 +558,22 @@ 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;
+	if (base->is_idle)
+		wake_up_nohz_cpu(base->cpu);
+}
+
+/*
+ * 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);
 
 	/* Check whether this is the new first expiring timer: */
 	if (time_after_eq(timer->expires, base->next_expiry))
@@ -578,21 +592,7 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
 	} else {
 		base->next_expiry = timer->expires;
 	}
-	wake_up_nohz_cpu(base->cpu);
-}
 
-/*
- * 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);
 	trigger_dyntick_cpu(base, timer);
 }
 
@@ -1490,7 +1490,6 @@ 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
@@ -1582,6 +1581,7 @@ 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:
@@ -1787,6 +1787,7 @@ 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);
@@ -2039,6 +2040,7 @@ 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);
 	}
 }
-- 
2.26.2