linux-kernel - Re: [PATCH] hrtimers: conditionally lock/unlock spinlock in hrtimer_get_next

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Date:	Mon, 9 Jun 2014 14:57:52 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Stanislav Fomichev <stfomichev@...dex-team.ru>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	stuart.w.hayes@...il.com, david.vrabel@...rix.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hrtimers: conditionally lock/unlock spinlock in hrtimer_get_next_event

On 9 June 2014 14:53, Stanislav Fomichev <stfomichev@...dex-team.ru> wrote:
> In hrtimer_get_next_event we unconditionally lock/unlock spinlock, even if it's
> not required (hrtimer_hres_active() != 0). This patch moves
> locking/unlocking and mindelta range check inside the if clause,
> so we don't execute unnecessary operations.
>
> Signed-off-by: Stanislav Fomichev <stfomichev@...dex-team.ru>
> ---
>  kernel/hrtimer.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
> index 39f339dcbe93..ce21e5f6bcf0 100644
> --- a/kernel/hrtimer.c
> +++ b/kernel/hrtimer.c
> @@ -1166,9 +1166,9 @@ ktime_t hrtimer_get_next_event(void)
>         unsigned long flags;
>         int i;
>
> -       raw_spin_lock_irqsave(&cpu_base->lock, flags);
> -
>         if (!hrtimer_hres_active()) {
> +               raw_spin_lock_irqsave(&cpu_base->lock, flags);
> +
>                 for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
>                         struct hrtimer *timer;
>                         struct timerqueue_node *next;
> @@ -1183,12 +1183,13 @@ ktime_t hrtimer_get_next_event(void)
>                         if (delta.tv64 < mindelta.tv64)
>                                 mindelta.tv64 = delta.tv64;
>                 }
> -       }
>
> -       raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> +               raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
> +
> +               if (mindelta.tv64 < 0)
> +                       mindelta.tv64 = 0;
> +       }
>
> -       if (mindelta.tv64 < 0)
> -               mindelta.tv64 = 0;
>         return mindelta;
>  }

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