linux-kernel - Re: [PATCH 1/2] sched/deadline: reduce overhead if there are no scheduling parameters changed

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Message-ID: <5474C119.7020800@arm.com>
Date:	Tue, 25 Nov 2014 17:49:13 +0000
From:	Juri Lelli <juri.lelli@....com>
To:	Wanpeng Li <wanpeng.li@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Kirill Tkhai <ktkhai@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/deadline: reduce overhead if there are no scheduling
 parameters changed

Hi,

On 19/11/14 08:35, Wanpeng Li wrote:
> There is no need to dequeue/enqueue and push/pull if there are
> no scheduling parameters changed for dl class, actually both 
> fair and rt class have already check if parameters changed for 
> them to avoid unnecessary overhead. This patch add the parameters 
> changed verify for dl class in order to reduce overhead.
> 
> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
> ---
>  kernel/sched/core.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 603c462..f361867 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3402,6 +3402,21 @@ static bool check_same_owner(struct task_struct *p)
>  	return match;
>  }
>  
> +static bool dl_param_changed(struct task_struct *p,
> +			const struct sched_attr *attr)

Please check alignment.

> +{
> +	struct sched_dl_entity *dl_se = &p->dl;
> +
> +	if (dl_se->dl_runtime != attr->sched_runtime ||
> +		dl_se->dl_deadline != attr->sched_deadline ||
> +		dl_se->dl_period != attr->sched_period ||
> +		dl_se->flags != attr->sched_flags ||
> +		p->rt_priority != attr->sched_priority)

This last one is useless, as we fail above if
attr->sched_priority != 0 when task has !rt_policy.

Thanks,

- Juri

> +		return true;
> +
> +	return false;
> +}
> +
>  static int __sched_setscheduler(struct task_struct *p,
>  				const struct sched_attr *attr,
>  				bool user)
> @@ -3530,7 +3545,7 @@ recheck:
>  			goto change;
>  		if (rt_policy(policy) && attr->sched_priority != p->rt_priority)
>  			goto change;
> -		if (dl_policy(policy))
> +		if (dl_policy(policy) && dl_param_changed(p, attr))
>  			goto change;
>  
>  		p->sched_reset_on_fork = reset_on_fork;
> 

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