linux-kernel - [PATCH v9 16/32] timers: Optimization for timer_base_try_to_set

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Message-Id: <20231201092654.34614-17-anna-maria@linutronix.de>
Date:   Fri,  1 Dec 2023 10:26:38 +0100
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Lukasz Luba <lukasz.luba@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH v9 16/32] timers: Optimization for timer_base_try_to_set_idle()

When tick is stopped also the timer base is_idle flag is set. When
reentering the 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
nohz_get_next_event() call which was executed before tick_nohz_stop_tick().

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
v9: New, as this optimization was splitted from the patch before.
---
 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 3e1cdb7c6966..c6b415052c56 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -886,7 +886,7 @@ 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 df6558f62e6f..177bcde8a2c0 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1996,13 +1996,18 @@ 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);
 }
 
-- 
2.39.2