linux-kernel - Re: [RFC PATCH 12/16 v3] Bias select wakee than waker in WAKE

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Date:	Tue, 3 Jun 2014 14:24:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	mingo@...hat.com, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	arjan.van.de.ven@...el.com, len.brown@...el.com,
	alan.cox@...el.com, mark.gross@...el.com, pjt@...gle.com,
	bsegall@...gle.com, morten.rasmussen@....com,
	vincent.guittot@...aro.org, rajeev.d.muralidhar@...el.com,
	vishwesh.m.rudramuni@...el.com, nicole.chalhoub@...el.com,
	ajaya.durg@...el.com, harinarayanan.seshadri@...el.com,
	jacob.jun.pan@...ux.intel.com, fengguang.wu@...el.com
Subject: Re: [RFC PATCH 12/16 v3] Bias select wakee than waker in WAKE_AFFINE

On Fri, May 30, 2014 at 02:36:08PM +0800, Yuyang Du wrote:
> In WAKE_AFFINE, we do not simply select idle, but bias wakee than waker
> if the cc of the wakee and waker (in this order) is capable of handling
> the wakee task
> 
> Signed-off-by: Yuyang Du <yuyang.du@...el.com>
> ---
>  kernel/sched/fair.c |   13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0c188df..d40ec9e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4370,7 +4370,18 @@ static int select_idle_sibling(struct task_struct *p, int target)
>  	struct sched_group *sg;
>  	int i = task_cpu(p);
>  
> -	if (idle_cpu(target))
> +	/*
> +	 * we do not select idle, if the cc of the wakee and
> +	 * waker (in this order) is capable of handling the wakee task
> +	 */
> +	if (sysctl_sched_cc_wakeup_threshold) {
> +		if (idle_cpu(i) || cpu_cc_capable(i))
> +			return i;
> +
> +		if (i != target && (idle_cpu(target) || cpu_cc_capable(target)))
> +			return target;
> +	}
> +	else if (idle_cpu(target))
>  		return target;
>  

So now you make a function called: select_idle_sibling() explicitly not
pick an idle cpu, and you don't think there's anything wrong with that?

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