linux-kernel - Re: [PATCH] timer: Lazily wakup nohz CPU when adding new timer.

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Date:	Sun, 11 Oct 2015 20:12:39 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] timer: Lazily wakup nohz CPU when adding new timer.

On Mon, 28 Sep 2015, Yunhong Jiang wrote:
>  static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
>  {
> +	bool kick_nohz = false;
> +
>  	/* Advance base->jiffies, if the base is empty */
>  	if (!base->all_timers++)
>  		base->timer_jiffies = jiffies;
> @@ -424,9 +426,17 @@ static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
>  	 */
>  	if (!(timer->flags & TIMER_DEFERRABLE)) {
>  		if (!base->active_timers++ ||
> -		    time_before(timer->expires, base->next_timer))
> +		    time_before(timer->expires, base->next_timer)) {
>  			base->next_timer = timer->expires;
> -	}
> +			/*
> +			 * CPU in dynticks need reevaluate the timer wheel
> +			 * if newer timer added with next_timer updated.
> +			 */
> +			if (base->nohz_active)
> +				kick_nohz = true;
> +		}
> +	} else if (base->nohz_active && tick_nohz_full_cpu(base->cpu))
> +		kick_nohz = true;

Why do you want to kick the other cpu when a deferrable timer got added?
  
Thanks,

	tglx
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