2024-01-24 17:09:36

by Frederic Weisbecker

Subject: [PATCH 09/15] tick: Move broadcast cancellation up to CPUHP_AP_TICK_DYING

The broadcast shutdown code is executed through a random explicit call
within stop machine from the outgoing CPU.

However The tick broadcast is a midware between the tick callback and
the clocksource, therefore it makes more sense to shut it down after the
tick callback and before the clocksource drivers.

Move it instead to the common tick shutdown CPU hotplug state where
related operations can be ordered from highest to lowest level.

Signed-off-by: Frederic Weisbecker <[email protected]>
---
include/linux/tick.h | 6 ------
kernel/cpu.c | 2 --
kernel/time/tick-common.c | 3 +++
kernel/time/tick-internal.h | 2 ++
4 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index afff4c207bd8..c7840ae8ebaf 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -73,12 +73,6 @@ extern void tick_broadcast_control(enum tick_broadcast_mode mode);
static inline void tick_broadcast_control(enum tick_broadcast_mode mode) { }
#endif /* BROADCAST */

-#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_HOTPLUG_CPU)
-extern void tick_offline_cpu(unsigned int cpu);
-#else
-static inline void tick_offline_cpu(unsigned int cpu) { }
-#endif
-
#ifdef CONFIG_GENERIC_CLOCKEVENTS
extern int tick_broadcast_oneshot_control(enum tick_broadcast_state state);
#else
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 263508073da8..5a8ad4f5ccf3 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1324,8 +1324,6 @@ static int take_cpu_down(void *_param)
*/
cpuhp_invoke_callback_range_nofail(false, cpu, st, target);

- /* Remove CPU from timer broadcasting */
- tick_offline_cpu(cpu);
/* Park the stopper thread */
stop_machine_park(cpu);
return 0;
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index b4af8c743b73..522414089c0d 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -412,6 +412,9 @@ int tick_cpu_dying(unsigned int dying_cpu)

tick_cancel_sched_timer(dying_cpu);

+ /* Remove CPU from timer broadcasting */
+ tick_offline_cpu(dying_cpu);
+
return 0;
}

diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 481b7ab65e2c..a939ff6de97c 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -137,8 +137,10 @@ static inline bool tick_broadcast_oneshot_available(void) { return tick_oneshot_
#endif /* !(BROADCAST && ONESHOT) */

#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_HOTPLUG_CPU)
+extern void tick_offline_cpu(unsigned int cpu);
extern void tick_broadcast_offline(unsigned int cpu);
#else
+static inline void tick_offline_cpu(unsigned int cpu) { }
static inline void tick_broadcast_offline(unsigned int cpu) { }
#endif

--
2.43.0

2024-01-25 10:07:42

by Thomas Gleixner

Subject: Re: [PATCH 09/15] tick: Move broadcast cancellation up to CPUHP_AP_TICK_DYING

On Wed, Jan 24 2024 at 18:04, Frederic Weisbecker wrote:
> The broadcast shutdown code is executed through a random explicit call
> within stop machine from the outgoing CPU.
>
> However The tick broadcast is a midware between the tick callback and

s/The/the/

> the clocksource, therefore it makes more sense to shut it down after the
> tick callback and before the clocksource drivers.
>
> Move it instead to the common tick shutdown CPU hotplug state where
> related operations can be ordered from highest to lowest level.
>
> Signed-off-by: Frederic Weisbecker <[email protected]>

Reviewed-by: Thomas Gleixner <[email protected]>