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

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 344b904..f6b6133 100644 (file)
--- 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 (file)
--- 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);
 }