linux-kernel - Re: [PATCH 4/9] timers: Always keep track of next expiry

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Date:   Tue, 14 Jul 2020 10:49:28 +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 4/9] timers: Always keep track of next expiry

Hi Frederic,

On Tue, 7 Jul 2020, Frederic Weisbecker wrote:

> So far next expiry was only tracked while the CPU was in nohz_idle mode
> in order to cope with missing ticks that can't increment the base->clk
> periodically anymore.
> 
> We are going to expand that logic beyond nohz in order to spare timers
> softirqs so do it unconditionally.
> 
> 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 | 36 +++++++++++++++++++-----------------
>  1 file changed, 19 insertions(+), 17 deletions(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index acf7cb8c09f8..8a4138e47aa4 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -558,8 +558,22 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
>  	 * timer is not deferrable. If the other CPU is on the way to idle
>  	 * then it can't set base->is_idle as we hold the base lock:
>  	 */
> -	if (!base->is_idle)
> -		return;
> +	if (base->is_idle)
> +		wake_up_nohz_cpu(base->cpu);
> +}
> +
> +/*
> + * Enqueue the timer into the hash bucket, mark it pending in
> + * the bitmap and store the index in the timer flags.
> + */
> +static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
> +			  unsigned int idx)
> +{
> +	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);
>  
>  	/* Check whether this is the new first expiring timer: */
>  	if (time_after_eq(timer->expires, base->next_expiry))
> @@ -578,21 +592,7 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
>  	} else {
>  		base->next_expiry = timer->expires;
>  	}
> -	wake_up_nohz_cpu(base->cpu);
> -}
>  
> -/*
> - * Enqueue the timer into the hash bucket, mark it pending in
> - * the bitmap and store the index in the timer flags.
> - */
> -static void enqueue_timer(struct timer_base *base, struct timer_list *timer,
> -			  unsigned int idx)
> -{
> -	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);
>  }
>  

Could you please split those two hunks which do only a restructuring into a
separate patch?

Thanks,

	Anna-Maria