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

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Message-ID: <CAOh2x=nOjzYQfyfdQ-sLN29echHZ5OhE1ygHk-MDqg_S1wv7Jw@mail.gmail.com>
Date:	Wed, 29 Apr 2015 08:11:58 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Joonwoo Park <joonwoop@...eaurora.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Saravana Kannan <skannan@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

On Tue, Apr 28, 2015 at 7:51 AM, Joonwoo Park <joonwoop@...eaurora.org> 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);
>  }

Oops !!

Fixes: 9f6d9baaa8ca ("timer: Kick dynticks targets on mod_timer*() calls")
Cc: 3.17+ <stable@...r.kernel.org> # 3.17+

Reviewed-by: Viresh Kumar <viresh.kumar@...aro.org>
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