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Date:   Wed, 13 Apr 2022 13:05:25 +0200
From:   Jan Kara <jack@suse.cz>
To:     Yu Kuai <yukuai3@huawei.com>
Cc:     tj@kernel.org, axboe@kernel.dk, paolo.valente@linaro.org,
        jack@suse.cz, cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com
Subject: Re: [PATCH -next 05/11] block, bfq: count root group into
 'num_groups_with_pending_reqs'
Message-ID: <20220413110525.u7wi2ttk5lag6r4b@quack3.lan>
References: <20220305091205.4188398-1-yukuai3@huawei.com>
 <20220305091205.4188398-6-yukuai3@huawei.com>
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On Sat 05-03-22 17:11:59, Yu Kuai wrote:
> Root group is not counted into 'num_groups_with_pending_reqs' because
> 'entity->parent' is set to NULL for child entities, thus
> for_each_entity() can't access root group.
> 
> This patch set root_group's entity to 'entity->parent' for child
> entities, this way root_group will be counted because for_each_entity()
> can access root_group in bfq_activate_requeue_entity(),
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/bfq-cgroup.c  | 6 +++---
>  block/bfq-iosched.h | 3 ++-
>  block/bfq-wf2q.c    | 5 +++++
>  3 files changed, 10 insertions(+), 4 deletions(-)

I think you can remove bfqg->my_entity after this patch, can't you? Because
effectively it's only purpose was so that you don't have to special-case
children of root_group...

								Honza

> 
> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> index 420eda2589c0..6cd65b5e790d 100644
> --- a/block/bfq-cgroup.c
> +++ b/block/bfq-cgroup.c
> @@ -436,7 +436,7 @@ void bfq_init_entity(struct bfq_entity *entity, struct bfq_group *bfqg)
>  		 */
>  		bfqg_and_blkg_get(bfqg);
>  	}
> -	entity->parent = bfqg->my_entity; /* NULL for root group */
> +	entity->parent = &bfqg->entity;
>  	entity->sched_data = &bfqg->sched_data;
>  }
>  
> @@ -581,7 +581,7 @@ static void bfq_group_set_parent(struct bfq_group *bfqg,
>  	struct bfq_entity *entity;
>  
>  	entity = &bfqg->entity;
> -	entity->parent = parent->my_entity;
> +	entity->parent = &parent->entity;
>  	entity->sched_data = &parent->sched_data;
>  }
>  
> @@ -688,7 +688,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>  	else if (bfqd->last_bfqq_created == bfqq)
>  		bfqd->last_bfqq_created = NULL;
>  
> -	entity->parent = bfqg->my_entity;
> +	entity->parent = &bfqg->entity;
>  	entity->sched_data = &bfqg->sched_data;
>  	/* pin down bfqg and its associated blkg  */
>  	bfqg_and_blkg_get(bfqg);
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index ddd8eff5c272..4530ab8b42ac 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -1024,13 +1024,14 @@ extern struct blkcg_policy blkcg_policy_bfq;
>  /* - interface of the internal hierarchical B-WF2Q+ scheduler - */
>  
>  #ifdef CONFIG_BFQ_GROUP_IOSCHED
> -/* stop at one of the child entities of the root group */
> +/* stop at root group */
>  #define for_each_entity(entity)	\
>  	for (; entity ; entity = entity->parent)
>  
>  #define is_root_entity(entity) \
>  	(entity->sched_data == NULL)
>  
> +/* stop at one of the child entities of the root group */
>  #define for_each_entity_not_root(entity) \
>  	for (; entity && !is_root_entity(entity); entity = entity->parent)
>  
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 17f1d2c5b8dc..138a2950b841 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -1125,6 +1125,11 @@ static void bfq_activate_requeue_entity(struct bfq_entity *entity,
>  {
>  	for_each_entity(entity) {
>  		bfq_update_groups_with_pending_reqs(entity);
> +
> +		/* root group is not in service tree */
> +		if (is_root_entity(entity))
> +			break;
> +
>  		__bfq_activate_requeue_entity(entity, non_blocking_wait_rq);
>  
>  		if (!bfq_update_next_in_service(entity->sched_data, entity,
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR