linux-kernel - Re: [PATCH] timers: consider slack value in mod

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Message-ID: <BANLkTinGZ0L4oQkBYo9H=R==X5Z+efjRaQ@mail.gmail.com>
Date:	Tue, 24 May 2011 15:54:17 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] timers: consider slack value in mod_timer()

On Sat, May 21, 2011 at 6:58 PM, Sebastian Andrzej Siewior
<sebastian@...akpoint.cc> wrote:
> There is an optimization which does not update the timer if the timer
> was pending and the expiration time was unchanged.
> Since commit 3bbb9ec9 ("timers: Introduce the concept of timer slack for
> legacy timers") this optimization is no longer applied for timers where
> the expiration time got extended due to the slack value. So here it adds
> the check again after the expiration time might have been updated.
>
> Signed-off-by: Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
> ---
>  kernel/timer.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/timer.c b/kernel/timer.c
> index fd61986..bf09726 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -804,6 +804,8 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
>                return 1;
>
>        expires = apply_slack(timer, expires);

So, why not move above line up, then we can use the recalculated
expires?

Thanks,
Yong

> +       if (timer_pending(timer) && timer->expires == expires)
> +               return 1;
>
>        return __mod_timer(timer, expires, false, TIMER_NOT_PINNED);
>  }
> --
> 1.7.4.4
>
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