[PATCH v2 1/2] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

[PATCH v2 1/2] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

[Peng Liu]

From: Peng Liu <liupeng17@lenovo.com>

The ts->sched_timer initialization work of tick_nohz_switch_to_nohz()
is almost the same as that of tick_setup_sched_timer(), so adjust the
latter to get it reused by tick_nohz_switch_to_nohz().

Signed-off-by: Peng Liu <liupeng17@lenovo.com>
---
Changes in v2:
- Fix build warning: Function parameter or member 'mode' not described in 'tick_setup_sched_timer'
- Fix build error: use of undeclared identifier 'tick_nohz_highres_handler'
- Fix build error: use of undeclared identifier 'sched_skew_tick'
---
 kernel/time/hrtimer.c    |  2 +-
 kernel/time/tick-sched.c | 37 ++++++++++++++++++-------------------
 kernel/time/tick-sched.h |  2 +-
 3 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 760793998cdd..355b5a957f7f 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -746,7 +746,7 @@ static void hrtimer_switch_to_hres(void)
 	base->hres_active = 1;
 	hrtimer_resolution = HIGH_RES_NSEC;
 
-	tick_setup_sched_timer();
+	tick_setup_sched_timer(NOHZ_MODE_HIGHRES);
 	/* "Retrigger" the interrupt to get things going */
 	retrigger_next_event(NULL);
 }
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index be77b021e5d6..96fcf5cb1b49 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1430,9 +1430,6 @@ static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
  */
 static void tick_nohz_switch_to_nohz(void)
 {
-	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
-	ktime_t next;
-
 	if (!tick_nohz_enabled)
 		return;
 
@@ -1441,16 +1438,9 @@ static void tick_nohz_switch_to_nohz(void)
 
 	/*
 	 * Recycle the hrtimer in 'ts', so we can share the
-	 * hrtimer_forward_now() function with the highres code.
+	 * highres code.
 	 */
-	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
-	/* Get the next period */
-	next = tick_init_jiffy_update();
-
-	hrtimer_set_expires(&ts->sched_timer, next);
-	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
-	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
-	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
+	tick_setup_sched_timer(NOHZ_MODE_LOWRES);
 }
 
 static inline void tick_nohz_irq_enter(void)
@@ -1529,7 +1519,9 @@ static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer)
 
 	return HRTIMER_RESTART;
 }
+#endif /* HIGH_RES_TIMERS */
 
+#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 static int sched_skew_tick;
 
 static int __init skew_tick(char *str)
@@ -1542,15 +1534,19 @@ early_param("skew_tick", skew_tick);
 
 /**
  * tick_setup_sched_timer - setup the tick emulation timer
+ * @mode: tick_nohz_mode to setup for
  */
-void tick_setup_sched_timer(void)
+void tick_setup_sched_timer(int mode)
 {
 	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
 	ktime_t now = ktime_get();
 
 	/* Emulate tick processing via per-CPU hrtimers: */
 	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
-	ts->sched_timer.function = tick_nohz_highres_handler;
+#ifdef CONFIG_HIGH_RES_TIMERS
+	if (mode == NOHZ_MODE_HIGHRES)
+		ts->sched_timer.function = tick_nohz_highres_handler;
+#endif
 
 	/* Get the next period (per-CPU) */
 	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
@@ -1564,12 +1560,15 @@ void tick_setup_sched_timer(void)
 	}
 
 	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
-	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
-	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
+#ifdef CONFIG_HIGH_RES_TIMERS
+	if (mode == NOHZ_MODE_HIGHRES)
+		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
+	else
+#endif
+		tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
+	tick_nohz_activate(ts, mode);
 }
-#endif /* HIGH_RES_TIMERS */
 
-#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 void tick_cancel_sched_timer(int cpu)
 {
 	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
@@ -1581,7 +1580,7 @@ void tick_cancel_sched_timer(int cpu)
 
 	memset(ts, 0, sizeof(*ts));
 }
-#endif
+#endif /* CONFIG_NO_HZ_COMMON || CONFIG_HIGH_RES_TIMERS */
 
 /*
  * Async notification about clocksource changes
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 5ed5a9d41d5a..35808bbb8a47 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -102,7 +102,7 @@ struct tick_sched {
 
 extern struct tick_sched *tick_get_tick_sched(int cpu);
 
-extern void tick_setup_sched_timer(void);
+extern void tick_setup_sched_timer(int mode);
 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 extern void tick_cancel_sched_timer(int cpu);
 #else
-- 
2.34.1

Re: [PATCH v2 1/2] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

[Frederic Weisbecker]

On Tue, Nov 28, 2023 at 05:23:54PM +0800, Peng Liu wrote:
> @@ -1529,7 +1519,9 @@ static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer)
>  
>  	return HRTIMER_RESTART;
>  }
> +#endif /* HIGH_RES_TIMERS */
>  
> +#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS

tick-sched.c is only ever built if CONFIG_TICK_ONESHOT=y and
CONFIG_TICK_ONESHOT is basically (CONFIG_NO_HZ_COMMON || CONFIG_HIGH_RES_TIMERS)

So probably the above is not needed and if you like you can even send
a subsequent patch removing such ifdefs within this file :-)

>  static int sched_skew_tick;
>  
>  static int __init skew_tick(char *str)
> @@ -1542,15 +1534,19 @@ early_param("skew_tick", skew_tick);
>  
>  /**
>   * tick_setup_sched_timer - setup the tick emulation timer
> + * @mode: tick_nohz_mode to setup for
>   */
> -void tick_setup_sched_timer(void)
> +void tick_setup_sched_timer(int mode)
>  {
>  	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
>  	ktime_t now = ktime_get();
>  
>  	/* Emulate tick processing via per-CPU hrtimers: */
>  	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
> -	ts->sched_timer.function = tick_nohz_highres_handler;
> +#ifdef CONFIG_HIGH_RES_TIMERS
> +	if (mode == NOHZ_MODE_HIGHRES)
> +		ts->sched_timer.function = tick_nohz_highres_handler;
> +#endif

That ifdef could simply be removed.

>  
>  	/* Get the next period (per-CPU) */
>  	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
> @@ -1564,12 +1560,15 @@ void tick_setup_sched_timer(void)
>  	}

That invisible part above is the skew_tick thing, which can probably work
on low-res mode so why not but please tell about that in the changelog.

>  
>  	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);

Looks like this can be hrtimer_forward_now() and you can remove the now.

> -	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
> -	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
> +#ifdef CONFIG_HIGH_RES_TIMERS
> +	if (mode == NOHZ_MODE_HIGHRES)
> +		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
> +	else
> +#endif

And probably that ifdef could simply be turned to
IS_ENABLED(CONFIG_HIGH_RES_TIMERS).

Thanks!

Re: [PATCH v2 1/2] tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()

[Peng Liu]

On 2023/11/29 0:56, Frederic Weisbecker wrote:
> On Tue, Nov 28, 2023 at 05:23:54PM +0800, Peng Liu wrote:
>> @@ -1529,7 +1519,9 @@ static enum hrtimer_restart tick_nohz_highres_handler(struct hrtimer *timer)
>>   
>>   	return HRTIMER_RESTART;
>>   }
>> +#endif /* HIGH_RES_TIMERS */
>>   
>> +#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
> tick-sched.c is only ever built if CONFIG_TICK_ONESHOT=y and
> CONFIG_TICK_ONESHOT is basically (CONFIG_NO_HZ_COMMON || CONFIG_HIGH_RES_TIMERS)
>
> So probably the above is not needed and if you like you can even send
> a subsequent patch removing such ifdefs within this file :-)
>
>>   static int sched_skew_tick;
>>   
>>   static int __init skew_tick(char *str)
>> @@ -1542,15 +1534,19 @@ early_param("skew_tick", skew_tick);
>>   
>>   /**
>>    * tick_setup_sched_timer - setup the tick emulation timer
>> + * @mode: tick_nohz_mode to setup for
>>    */
>> -void tick_setup_sched_timer(void)
>> +void tick_setup_sched_timer(int mode)
>>   {
>>   	struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
>>   	ktime_t now = ktime_get();
>>   
>>   	/* Emulate tick processing via per-CPU hrtimers: */
>>   	hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
>> -	ts->sched_timer.function = tick_nohz_highres_handler;
>> +#ifdef CONFIG_HIGH_RES_TIMERS
>> +	if (mode == NOHZ_MODE_HIGHRES)
>> +		ts->sched_timer.function = tick_nohz_highres_handler;
>> +#endif
> That ifdef could simply be removed.
>
>>   
>>   	/* Get the next period (per-CPU) */
>>   	hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
>> @@ -1564,12 +1560,15 @@ void tick_setup_sched_timer(void)
>>   	}
> That invisible part above is the skew_tick thing, which can probably work
> on low-res mode so why not but please tell about that in the changelog.
>
>>   
>>   	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);
> Looks like this can be hrtimer_forward_now() and you can remove the now.
>
>> -	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
>> -	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
>> +#ifdef CONFIG_HIGH_RES_TIMERS
>> +	if (mode == NOHZ_MODE_HIGHRES)
>> +		hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
>> +	else
>> +#endif
> And probably that ifdef could simply be turned to
> IS_ENABLED(CONFIG_HIGH_RES_TIMERS).
>
> Thanks!
Thanks for comments. I will update my patches, and also try removing
(CONFIG_NO_HZ_COMMON || CONFIG_HIGH_RES_TIMERS) in another patch.

Regards,
Peng