linux-kernel - Re: [PATCH 07/20] blkio: Provide capablity to enqueue/dequeue group entities

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Date:	Wed, 04 Nov 2009 10:34:57 -0500
From:	Jeff Moyer <jmoyer@...hat.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,
	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
Subject: Re: [PATCH 07/20] blkio: Provide capablity to enqueue/dequeue group entities

Vivek Goyal <vgoyal@...hat.com> writes:

> o This patch embeds cfq_entity object in cfq_group and provides helper routines
>   so that group entities can be scheduled.
>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
>  block/cfq-iosched.c |  110 +++++++++++++++++++++++++++++++++++++++++++--------
>  1 files changed, 93 insertions(+), 17 deletions(-)
>
> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
> index bc99163..8ec8a82 100644
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -79,6 +79,7 @@ struct cfq_service_tree {
>  #define CFQ_RB_ROOT	(struct cfq_service_tree) { RB_ROOT, NULL, 0, NULL}
>  
>  struct cfq_sched_data {
> +	unsigned int nr_active;
>  	struct cfq_service_tree service_tree[IO_IOPRIO_CLASSES];
>  };
>  
> @@ -89,6 +90,10 @@ struct cfq_entity {
>  	struct cfq_service_tree *st;
>  	unsigned short ioprio_class;
>  	bool ioprio_class_changed;
> +	struct cfq_entity *parent;
> +	bool on_st;
> +	/* Points to the sched_data of group entity. Null for cfqq */
> +	struct cfq_sched_data *my_sd;

Why my_sd?  None of the other members required a my.  ;-)

> +static inline struct cfq_entity *parent_entity(struct cfq_entity *cfqe)
> +{
> +	return cfqe->parent;
> +}

Wow, is this really necessary for a pointer dereference?

> +#ifdef CONFIG_CFQ_GROUP_IOSCHED
> +/* check for entity->parent so that loop is not executed for root entity. */
> +#define for_each_entity(entity)	\
> +	for (; entity && entity->parent; entity = entity->parent)

See, you don't use it here!

> @@ -660,7 +723,13 @@ static void enqueue_cfqe(struct cfq_entity *cfqe)
>  
>  static void enqueue_cfqq(struct cfq_queue *cfqq)
>  {
> -	enqueue_cfqe(&cfqq->entity);
> +	struct cfq_entity *cfqe = &cfqq->entity;
> +
> +	for_each_entity(cfqe) {
> +		if (cfqe->on_st)
> +			break;
> +		enqueue_cfqe(cfqe);
> +	}
>  }

Maybe I'm slow, but I would have benefitted from a comment above that
function stating that we have to walk up the tree to make sure that the
parent is also scheduled.

Cheers,
Jeff
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