linux-kernel - [RFC PATCH 05/10] timers: Always keep track of next expiry

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Date:   Wed,  1 Jul 2020 03:10:25 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: [RFC PATCH 05/10] timers: Always keep track of next expiry

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@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
Cc: Juri Lelli <juri.lelli@...hat.com>
---
 kernel/time/timer.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 4aa74aafdd33..30f491ec875a 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -550,8 +550,22 @@ 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))
@@ -570,21 +584,7 @@ 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);
 }
 
@@ -1482,7 +1482,6 @@ 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
@@ -1574,6 +1573,7 @@ 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:
@@ -1779,6 +1779,7 @@ 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);
-- 
2.26.2