linux-kernel - [tip: timers/core] timers: Optimization for timer_base_try_to_set

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Date: Thu, 22 Feb 2024 17:12:15 -0000
From: "tip-bot2 for Anna-Maria Behnsen" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Anna-Maria Behnsen" <anna-maria@...utronix.de>,
 Thomas Gleixner <tglx@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: timers/core] timers: Optimization for timer_base_try_to_set_idle()

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     73129cf4b69cd1aaa3dd5eb7900a9c349773f5ae
Gitweb:        https://git.kernel.org/tip/73129cf4b69cd1aaa3dd5eb7900a9c349773f5ae
Author:        Anna-Maria Behnsen <anna-maria@...utronix.de>
AuthorDate:    Wed, 21 Feb 2024 10:05:32 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 22 Feb 2024 17:52:30 +01:00

timers: Optimization for timer_base_try_to_set_idle()

When tick is stopped also the timer base is_idle flag is set. When
reentering timer_base_try_to_set_idle() with the tick stopped, there is no
need to check whether the timer base needs to be set idle again. When a
timer was enqueued in the meantime, this is already handled by the
tick_nohz_next_event() call which was executed before
tick_nohz_stop_tick().

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20240221090548.36600-5-anna-maria@linutronix.de

---
 kernel/time/tick-sched.c |  2 +-
 kernel/time/timer.c      | 11 ++++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 344b904..f6b6133 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -896,7 +896,7 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
 	unsigned long basejiff = ts->last_jiffies;
 	u64 basemono = ts->timer_expires_base;
-	bool timer_idle;
+	bool timer_idle = ts->tick_stopped;
 	u64 expires;
 
 	/* Make sure we won't be trying to stop it twice in a row. */
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a4b8a58..74cfe21 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2044,13 +2044,18 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
  * timer_base_try_to_set_idle() - Try to set the idle state of the timer bases
  * @basej:	base time jiffies
  * @basem:	base time clock monotonic
- * @idle:	pointer to store the value of timer_base->is_idle
+ * @idle:	pointer to store the value of timer_base->is_idle on return;
+ *		*idle contains the information whether tick was already stopped
  *
- * Returns the tick aligned clock monotonic time of the next pending
- * timer or KTIME_MAX if no timer is pending.
+ * Returns the tick aligned clock monotonic time of the next pending timer or
+ * KTIME_MAX if no timer is pending. When tick was already stopped KTIME_MAX is
+ * returned as well.
  */
 u64 timer_base_try_to_set_idle(unsigned long basej, u64 basem, bool *idle)
 {
+	if (*idle)
+		return KTIME_MAX;
+
 	return __get_next_timer_interrupt(basej, basem, idle);
 }