linux-kernel - Re: [PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

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Date:	Tue, 28 Apr 2015 14:59:04 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Joonwoo Park <joonwoop@...eaurora.org>, tglx@...utronix.de
CC:	skannan@...eaurora.org, linux-kernel@...r.kernel.org,
	John Stultz <john.stultz@...aro.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

On 04/27/15 19:21, Joonwoo Park wrote:
> At present, internal_add_timer() examines flags with 'base' which doesn't
> contain flags.  Examine with 'timer->base' to avoid unnecessary waking up
> of nohz CPU when timer base has TIMER_DEFERRABLE.
>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: John Stultz <john.stultz@...aro.org>
> Signed-off-by: Joonwoo Park <joonwoop@...eaurora.org>
> ---
>  kernel/time/timer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 2ece3aa..e5d5733c 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -434,7 +434,7 @@ static void internal_add_timer(struct tvec_base *base, struct timer_list *timer)
>  	 * require special care against races with idle_cpu(), lets deal
>  	 * with that later.
>  	 */
> -	if (!tbase_get_deferrable(base) || tick_nohz_full_cpu(base->cpu))
> +	if (!tbase_get_deferrable(timer->base) || tick_nohz_full_cpu(base->cpu))
>  		wake_up_nohz_cpu(base->cpu);
>  }
>  

This looks like a fix for commit 9f6d9baaa8ca (timer: Kick dynticks
targets on mod_timer*() calls, 2014-06-22) which changed the code to use
base instead of timer->base when it moved this condition from
add_timer_on() into internal_add_timer(). Is that right?

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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