[PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

[PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

[Joonwoo Park]

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@linutronix.de>
CC: John Stultz <john.stultz@linaro.org>
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.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);
 }
 
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Re: [PATCH 1/2] timer: avoid unnecessary waking up of nohz CPU

[Stephen Boyd]

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@linutronix.de>
> CC: John Stultz <john.stultz@linaro.org>
> Signed-off-by: Joonwoo Park <joonwoop@codeaurora.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

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

[Viresh Kumar]

On Tue, Apr 28, 2015 at 7:51 AM, Joonwoo Park <joonwoop@codeaurora.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@linutronix.de>
> CC: John Stultz <john.stultz@linaro.org>
> Signed-off-by: Joonwoo Park <joonwoop@codeaurora.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@vger.kernel.org> # 3.17+

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

[tip:timers/core] timer: Use timer->base for flag checks

[tip-bot for Joonwoo Park]

Commit-ID:  781978e6e156101209f62b9ebc8783b70ef248de
Gitweb:     http://git.kernel.org/tip/781978e6e156101209f62b9ebc8783b70ef248de
Author:     Joonwoo Park <joonwoop@codeaurora.org>
AuthorDate: Mon, 27 Apr 2015 19:21:49 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 5 May 2015 10:40:43 +0200

timer: Use timer->base for flag checks

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 set.

Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
Cc: sboyd@codeaurora.org
Cc: skannan@codeaurora.org
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/1430187709-21087-1-git-send-email-joonwoop@codeaurora.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 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 03f926c..d4af7c5 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -436,7 +436,7 @@ 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);
 }