linux-kernel - Re: [PATCH 02/16] blkio: Keep queue on service tree until we expire it

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Date:	Tue, 17 Nov 2009 13:07:40 -0500
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	m-ikeda@...jp.nec.com, akpm@...ux-foundation.org, riel@...hat.com,
	kamezawa.hiroyu@...fujitsu.com, czoccolo@...il.com
Subject: Re: [PATCH 02/16] blkio: Keep queue on service tree until we
 expire it

Hi Vivek - 

Some minor nit comments in this and the next three e-mails...

On Fri, 2009-11-13 at 12:40 -0500, Vivek Goyal wrote:

> @@ -1065,17 +1080,43 @@ static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
>   * Get next queue for service. Unless we have a queue preemption,
>   * we'll simply select the first cfqq in the service tree.
>   */
> -static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
> +static struct cfq_queue *__cfq_get_next_queue(struct cfq_data *cfqd)
>  {
>  	struct cfq_rb_root *service_tree =
>  		service_tree_for(cfqd->serving_group, cfqd->serving_prio,
>  					cfqd->serving_type, cfqd);
>  
> +	if (!cfqd->rq_queued)
> +		return NULL;
> +
>  	if (RB_EMPTY_ROOT(&service_tree->rb))
>  		return NULL;
>  	return cfq_rb_first(service_tree);
>  }
>  
> +static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
> +{
> +	struct cfq_group *cfqg = &cfqd->root_group;
> +	struct cfq_queue *cfqq;
> +	int i, j;
> +
> +	if (!cfqd->rq_queued)
> +		return NULL;
> +
> +	for (i = 0; i < 2; ++i) {
> +		for (j = 0; j < 3; ++j) {

Is this double for-loop a good candidate for an iterator macro
construct? (I think this is used 6 times in your total patch set.)
 
> +			cfqq = cfq_rb_first(&cfqg->service_trees[i][j]);
> +			if (cfqq)
> +				return cfqq;
> +		}
> +	}
> +

Perhaps just change the 4 lines below with:

	return cfq_rb_first(&cfgg->service_tree_idle);

to be consistent (e.g. right above in __cfq_get_next_queue) and for less
code clutter?

> +	cfqq = cfq_rb_first(&cfqg->service_tree_idle);
> +	if (cfqq)
> +		return cfqq;
> +	return NULL;
> +}
> +


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