linux-kernel - Re: [PATCH v6 07/21] timers: Introduce add_timer() variants which modify timer flags

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Date:   Mon, 5 Jun 2023 23:43:18 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Rik van Riel <riel@...riel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sebastian Siewior <bigeasy@...utronix.de>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Lukasz Luba <lukasz.luba@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>
Subject: Re: [PATCH v6 07/21] timers: Introduce add_timer() variants which
 modify timer flags

Le Wed, May 10, 2023 at 09:28:03AM +0200, Anna-Maria Behnsen a écrit :
> Timer might be used as pinned timer (using add_timer_on()) and later on as
> non pinned timers using add_timer(). When the NOHZ timer pull at expiry
> model is in place, TIMER_PINNED flag is required to be used whenever a
> timer needs to expire on a dedicated CPU. Flag must no be set, if
> expiration on a dedicated CPU is not required.
> 
> add_timer_on()'s behavior will be changed during the preparation patches
> for the NOHZ timer pull at expiry model to unconditionally set TIMER_PINNED
> flag. To be able to reset/set the flag when queueing a timer, two variants
> of add_timer() are introduced.
> 
> This is a preparatory patch and has no functional change.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
> ---
> New in v6
> ---
>  include/linux/timer.h |  2 ++
>  kernel/time/timer.c   | 34 ++++++++++++++++++++++++++++++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/include/linux/timer.h b/include/linux/timer.h
> index 9162f275819a..6f96661480dd 100644
> --- a/include/linux/timer.h
> +++ b/include/linux/timer.h
> @@ -180,6 +180,8 @@ extern int timer_reduce(struct timer_list *timer, unsigned long expires);
>  #define NEXT_TIMER_MAX_DELTA	((1UL << 30) - 1)
>  
>  extern void add_timer(struct timer_list *timer);
> +extern void add_timer_local(struct timer_list *timer);
> +extern void add_timer_global(struct timer_list *timer);
>  
>  extern int try_to_del_timer_sync(struct timer_list *timer);
>  extern int timer_delete_sync(struct timer_list *timer);
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 1522fb81887e..ab9a8bb11a8a 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1242,6 +1242,40 @@ void add_timer(struct timer_list *timer)
>  }
>  EXPORT_SYMBOL(add_timer);
>  
> +/**
> + * add_timer_local - Start a timer on the local CPU
> + * @timer:	The timer to be started
> + *
> + * Same as add_timer() except that the timer flag TIMER_PINNED is set.
> + *
> + * See add_timer() for further details.
> + */
> +void add_timer_local(struct timer_list *timer)
> +{
> +	if (WARN_ON_ONCE(timer_pending(timer)))
> +		return;
> +	timer->flags |= TIMER_PINNED;
> +	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
> +}
> +EXPORT_SYMBOL(add_timer_local);

This one doesn't seem to be used at the end of the patchset.

Thanks.