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Subject[tip: timers/core] timers: Always keep track of next expiry
The following commit has been merged into the timers/core branch of tip:

Commit-ID: dc2a0f1fb2a06df09f5094f29aea56b763aa7cca
Gitweb: https://git.kernel.org/tip/dc2a0f1fb2a06df09f5094f29aea56b763aa7cca
Author: Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Fri, 17 Jul 2020 16:05:46 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Fri, 17 Jul 2020 21:55:23 +02:00

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.

This logic is going to be expanded beyond nohz in order to spare timer
softirqs so do it unconditionally.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200717140551.29076-8-frederic@kernel.org

---
kernel/time/timer.c | 42 +++++++++++++++++++++---------------------
1 file changed, 21 insertions(+), 21 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 9abc417..76fd964 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -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);
}
}
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