diff mbox series

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

Message ID 20240115143743.27827-5-anna-maria@linutronix.de
State New
Headers
Series timers: Move from a push remote at enqueue to a pull at expiry model |

Commit Message

Anna-Maria Behnsen Jan. 15, 2024, 2:37 p.m. UTC 
  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(-)

Comments

Frederic Weisbecker Jan. 17, 2024, 4:45 p.m. UTC | #1 
Le Mon, Jan 15, 2024 at 03:37:27PM +0100, Anna-Maria Behnsen a écrit :
> 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;

Ok now I see the reason behind the behavioural change.

So either:

* We remove the old behaviour consisting in clearing base->is_idle if the new
  next timer is within a jiffy while the tick is stopped. But then the changelog
  from the previous patch should state that and comments must be clarified.

or:

* We restore the old behaviour, making things a bit more complicated I guess.

Thanks.
Anna-Maria Behnsen Jan. 22, 2024, 11:48 a.m. UTC | #2 
Frederic Weisbecker <frederic@kernel.org> writes:

> Le Mon, Jan 15, 2024 at 03:37:27PM +0100, Anna-Maria Behnsen a écrit :
>> 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;
>
> Ok now I see the reason behind the behavioural change.
>
> So either:
>
> * We remove the old behaviour consisting in clearing base->is_idle if the new
>   next timer is within a jiffy while the tick is stopped. But then the changelog
>   from the previous patch should state that and comments must be clarified.
>

I would like to take 'either'. I thought the changelog already mentioned
it. But maybe I have to make it more explicit. I'll go and rework the
comments once more.

Thanks,

	Anna-Maria
Frederic Weisbecker Jan. 22, 2024, 10:22 p.m. UTC | #3 
Le Mon, Jan 15, 2024 at 03:37:27PM +0100, Anna-Maria Behnsen a écrit :
> 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>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
diff mbox series

Patch

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);
 }