linux-kernel - Re: [PATCH v2 3/6] sched: don't consider other cpus in our group in case of NEWLY

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Date:	Mon, 22 Apr 2013 13:59:47 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2 3/6] sched: don't consider other cpus in our group in
 case of NEWLY_IDLE

On Tue, 2013-03-26 at 15:01 +0900, Joonsoo Kim wrote:
> Commit 88b8dac0 makes load_balance() consider other cpus in its group,
> regardless of idle type. When we do NEWLY_IDLE balancing, we should not
> consider it, because a motivation of NEWLY_IDLE balancing is to turn
> this cpu to non idle state if needed. This is not the case of other cpus.
> So, change code not to consider other cpus for NEWLY_IDLE balancing.
> 
> With this patch, assign 'if (pulled_task) this_rq->idle_stamp = 0'
> in idle_balance() is corrected, because NEWLY_IDLE balancing doesn't
> consider other cpus. Assigning to 'this_rq->idle_stamp' is now valid.
> 
> Cc: Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
> Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 9d693d0..3f8c4f2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5007,8 +5007,17 @@ static int load_balance(int this_cpu, struct rq *this_rq,
>  		.cpus		= cpus,
>  	};
>  
> +	/* For NEWLY_IDLE load_balancing, we don't need to consider
> +	 * other cpus in our group */
> +	if (idle == CPU_NEWLY_IDLE) {
> +		env.dst_grpmask = NULL;
> +		/* we don't care max_lb_iterations in this case,
> +		 * in following patch, this will be removed */

This comment violates coding style; comments looks like:

  /* this is a single-line comment */

or

  /*
   * this is a multi-
   *                 line comment.
   */

Luckily you're deleting these offensive lines again in patch 6 :-)

> +		max_lb_iterations = 0;
> +	} else {
> +		max_lb_iterations = cpumask_weight(env.dst_grpmask);
> +	}
>  	cpumask_copy(cpus, cpu_active_mask);
> -	max_lb_iterations = cpumask_weight(env.dst_grpmask);
>  
>  	schedstat_inc(sd, lb_count[idle]);
>  


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