[PATCH v10 04/20] timers: Optimization for timer_base_try_to_set_idle()

Anna-Maria Behnsen
2024-01-15T14:38:06Z

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
tick_nohz_next_event() call which was executed before
tick_nohz_stop_tick().

Signed-off-by: Anna-Maria Behnsen <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 c6223afc801f..27f1a2ae7f39 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 3a668060692e..2f69a485a070 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1999,13 +1999,18 @@ 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