linux-kernel - Re: [PATCH 1/9] timer: Move trigger_dyntick_cpu() to enqueue

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Message-ID: <alpine.DEB.2.21.2007091312340.4020@somnus>
Date:   Thu, 9 Jul 2020 14:17:35 +0200 (CEST)
From:   Anna-Maria Behnsen <anna-maria@...utronix.de>
To:     Frederic Weisbecker <frederic@...nel.org>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH 1/9] timer: Move trigger_dyntick_cpu() to
 enqueue_timer()

Hi Frederic,

On Tue, 7 Jul 2020, Frederic Weisbecker wrote:

> Consolidate the code by calling trigger_dyntick_cpu() from
> enqueue_timer() instead of calling it from all its callers.

Looks good, but maybe you could also update the comments in the code (see
remarks below)?

> Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Juri Lelli <juri.lelli@...hat.com>
> ---
>  kernel/time/timer.c | 46 +++++++++++++++++++--------------------------
>  1 file changed, 19 insertions(+), 27 deletions(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 9a838d38dbe6..4c977df3610b 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -596,13 +573,29 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
>  	wake_up_nohz_cpu(base->cpu);
>  }
>  
> -static void
> -internal_add_timer(struct timer_base *base, struct timer_list *timer)
> +/*
> + * Enqueue the timer into the hash bucket, mark it pending in
> + * the bitmap and store the index in the timer flags.
> + */

enqueue_timer() also calls trigger_dyntick_cpu().

> +static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
> +			  unsigned int idx)
>  {
> -	__internal_add_timer(base, timer);
> +	hlist_add_head(&timer->entry, base->vectors + idx);
> +	__set_bit(idx, base->pending_map);
> +	timer_set_idx(timer, idx);
> +
> +	trace_timer_start(timer, timer->expires, timer->flags);
>  	trigger_dyntick_cpu(base, timer);
>  }
>  
> +static void internal_add_timer(struct timer_base *base, struct timer_list *timer)
> +{
> +	unsigned int idx;
> +
> +	idx = calc_wheel_index(timer->expires, base->clk);
> +	enqueue_timer(base, timer, idx);
> +}
> +
>  #ifdef CONFIG_DEBUG_OBJECTS_TIMERS
>  
>  static struct debug_obj_descr timer_debug_descr;
> @@ -1059,7 +1052,6 @@ __mod_timer(struct timer_list *timer, unsigned long expires, unsigned int option
>  	 */

The comment above still mentions that trigger_dyntick_cpu() is called which
is now part of enqueue_timer(). Might be a little confusing.

>  	if (idx != UINT_MAX && clk == base->clk) {
>  		enqueue_timer(base, timer, idx);
> -		trigger_dyntick_cpu(base, timer);
>  	} else {
>  		internal_add_timer(base, timer);
>  	}


Thanks,

	Anna-Maria