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

Frederic Weisbecker
2020-07-01T01:10:49Z

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@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.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