linux-kernel - Re: [PATCH tip/core/timers 2/4] timers: Reduce __run

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Message-ID: <20140115203354.GC11147@jtriplet-mobl1>
Date:	Wed, 15 Jan 2014 12:33:55 -0800
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	darren@...art.com, fweisbec@...il.com, oleg@...hat.com, sbw@....edu
Subject: Re: [PATCH tip/core/timers 2/4] timers: Reduce __run_timers()
 latency for empty list

On Tue, Jan 14, 2014 at 09:20:46PM -0800, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> The __run_timers() function currently steps through the list one jiffy at
> a time in order to update the timer wheel.  However, if the timer wheel
> is empty, no adjustment is needed other than updating ->timer_jiffies.
> In this case, which is likely to be common for NO_HZ_FULL kernels, the
> kernel currently incurs a large latency for no good reason.  This commit
> therefore short-circuits this case.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  kernel/timer.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/timer.c b/kernel/timer.c
> index 2245b7374c3d..295837e5e011 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -338,6 +338,17 @@ void set_timer_slack(struct timer_list *timer, int slack_hz)
>  }
>  EXPORT_SYMBOL_GPL(set_timer_slack);
>  
> +static bool catchup_timer_jiffies(struct tvec_base *base)
> +{
> +#ifdef CONFIG_NO_HZ_FULL
> +	if (!base->all_timers) {
> +		base->timer_jiffies = jiffies;
> +		return 1;
> +	}
> +#endif /* #ifdef CONFIG_NO_HZ_FULL */
> +	return 0;
> +}

In a function with return type "bool", please use true/false, not 1/0.

Please also document the semantic of the return value.

- Josh Triplett
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