linux-kernel - Re: [PATCH] sched: add a tuning knob to allow changing RR tmeslice

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Date:	Wed, 23 Jan 2013 15:09:38 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Clark Williams <williams@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: add a tuning knob to allow changing RR tmeslice

On Thu, 2012-11-08 at 14:27 -0600, Clark Williams wrote:
> Subject: [PATCH] sched: add a tuning knob to allow changing RR timeslice
> 
> User wanted a facility simliar to the ability on Solaris to adjust
> the SCHED_RR timeslice value. Add a /proc/sys/kernel scheduler knob
> named sched_rr_timeslice_ms which allows global changing of the SCHED_RR
> timeslice value. User visable value is in milliseconds but is stored as
> jiffies.  Setting to 0 (zero) resets to the default (currently 100ms).
> 

Hmm, has this been ignored?

I guess the real question, is it still needed (or wanted)?

-- Steve

> Patch against tip/master, currently 3.7-rc3.
> 
> Signed-off-by: Clark Williams <williams@...hat.com>
> ---
>  include/linux/sched.h |  6 +++++-
>  kernel/sched.c        | 19 +++++++++++++++++++
>  kernel/sched_rt.c     |  4 ++--
>  kernel/sysctl.c       |  8 ++++++++
>  4 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 12317b6..214bf27 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2097,11 +2097,15 @@ static inline unsigned int get_sysctl_timer_migration(void)
>  #endif
>  extern unsigned int sysctl_sched_rt_period;
>  extern int sysctl_sched_rt_runtime;
> -
>  int sched_rt_handler(struct ctl_table *table, int write,
>  		void __user *buffer, size_t *lenp,
>  		loff_t *ppos);
>  
> +extern int sched_rr_timeslice;
> +extern int sched_rr_handler(struct ctl_table *table, int write,
> +		void __user *buffer, size_t *lenp,
> +		loff_t *ppos);
> +
>  #ifdef CONFIG_SCHED_AUTOGROUP
>  extern unsigned int sysctl_sched_autogroup_enabled;
>  
> diff --git a/kernel/sched.c b/kernel/sched.c
> index cdf9484..c63c3a4 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -120,6 +120,7 @@
>   * Timeslices get refilled after they expire.
>   */
>  #define DEF_TIMESLICE		(100 * HZ / 1000)
> +int sched_rr_timeslice = DEF_TIMESLICE;
>  
>  /*
>   * single value that denotes runtime == period, ie unlimited time.
> @@ -9614,6 +9615,24 @@ static int sched_rt_global_constraints(void)
>  }
>  #endif /* CONFIG_RT_GROUP_SCHED */
>  
> +int sched_rr_handler(struct ctl_table *table, int write,
> +		void __user *buffer, size_t *lenp,
> +		loff_t *ppos)
> +{
> +	int ret;
> +	static DEFINE_MUTEX(mutex);
> +
> +	mutex_lock(&mutex);
> +	ret = proc_dointvec(table, write, buffer, lenp, ppos);
> +	/* make sure that internally we keep jiffies */
> +	/* also, writing zero resets timeslice to default */
> +	if (!ret && write) 
> +		sched_rr_timeslice = sched_rr_timeslice <= 0 ? 
> +			DEF_TIMESLICE : msecs_to_jiffies(sched_rr_timeslice);
> +	mutex_unlock(&mutex);
> +	return ret;
> +}
> +
>  int sched_rt_handler(struct ctl_table *table, int write,
>  		void __user *buffer, size_t *lenp,
>  		loff_t *ppos)
> diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
> index c108b9c..799dd09 100644
> --- a/kernel/sched_rt.c
> +++ b/kernel/sched_rt.c
> @@ -1791,7 +1791,7 @@ static void task_tick_rt(struct rq *rq, struct task_struct *p, int queued)
>  	if (--p->rt.time_slice)
>  		return;
>  
> -	p->rt.time_slice = DEF_TIMESLICE;
> +	p->rt.time_slice = sched_rr_timeslice;
>  
>  	/*
>  	 * Requeue to the end of queue if we are not the only element
> @@ -1819,7 +1819,7 @@ static unsigned int get_rr_interval_rt(struct rq *rq, struct task_struct *task)
>  	 * Time slice is 0 for SCHED_FIFO tasks
>  	 */
>  	if (task->policy == SCHED_RR)
> -		return DEF_TIMESLICE;
> +		return sched_rr_timeslice;
>  	else
>  		return 0;
>  }
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ea7ec7f..10b1129 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -362,6 +362,14 @@ static struct ctl_table kern_table[] = {
>  		.mode		= 0644,
>  		.proc_handler	= sched_rt_handler,
>  	},
> +	{
> +		.procname	= "sched_rr_timeslice_ms",
> +		.data		= &sched_rr_timeslice,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= sched_rr_handler,
> +	},
> +
>  #ifdef CONFIG_SCHED_AUTOGROUP
>  	{
>  		.procname	= "sched_autogroup_enabled",


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