Re: [PATCH v2 1/4] block, bfq: add support to track if root_group have any pending requests

[Paolo Valente <paolo.valente@linaro.org>]

> Il giorno 6 ago 2021, alle ore 04:08, Yu Kuai <yukuai3@huawei.com> ha scritto:
> 
> Add a new member in bfq_data to track number of queues that are in
> root_group with any pending requests.

maybe modify the last part of the sentence as: ... and that have some pending request

> This will be used in next patch
> to optmize queue idle judgment when root_group doesn't have any
> pending requests.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
> block/bfq-iosched.c |  8 +++++++-
> block/bfq-iosched.h | 13 +++++++++++--
> block/bfq-wf2q.c    | 37 ++++++++++++++++++++++++-------------
> 3 files changed, 42 insertions(+), 16 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 727955918563..7c6b412f9a9c 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -859,8 +859,14 @@ void __bfq_weights_tree_remove(struct bfq_data *bfqd,
> void bfq_weights_tree_remove(struct bfq_data *bfqd,
> 			     struct bfq_queue *bfqq)
> {
> -	struct bfq_entity *entity = bfqq->entity.parent;
> +	struct bfq_entity *entity = &bfqq->entity;
> +
> +	if (entity->in_groups_with_pending_reqs) {
> +		entity->in_groups_with_pending_reqs = false;
> +		bfqd->num_queues_with_pending_reqs_in_root--;

Here you cross the comment "The decrement of
num_groups_with_pending_reqs is not performed immediately upon ...".

Find a way to
- move that comment up, and to make it correct for this slightly
  different decrement
- leave a correct comment (probably shorter) in the original position

> +	}
> 
> +	entity = entity->parent;
> 	for_each_entity(entity) {
> 		struct bfq_sched_data *sd = entity->my_sched_data;
> 
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 99c2a3cb081e..610769214f72 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -195,7 +195,12 @@ struct bfq_entity {
> 	/* flag, set to request a weight, ioprio or ioprio_class change  */
> 	int prio_changed;
> 
> -	/* flag, set if the entity is counted in groups_with_pending_reqs */
> +	/*
> +	 * If entity represents bfq_group, this flag will set

will be set?

> if the group is
> +	 * not root_group and have

has

> any pending requests; If entity represents

one more nit: use lowercase after semicolon

> +	 * bfq_queue, this flag will set

will be set

> if the queue is in root_group and have
> +	 * any pending requests.
> +	 */
> 	bool in_groups_with_pending_reqs;
> 

The name of the above field follows from the fact that entity is
counted in groups_with_pending_reqs.  You change this fact, because,
in your patch, a queue is not counted in groups_with_pending_reqs.
But you leave the same name. This creates confusion.


> 	/* last child queue of entity created (for non-leaf entities) */
> @@ -539,7 +544,11 @@ struct bfq_data {
> 	 * with no request waiting for completion.
> 	 */
> 	unsigned int num_groups_with_pending_reqs;
> -
> +	/*
> +	 * number of queues that are in root_group with at least one request
> +	 * waiting for completion.

please link somehow this comment to the long comment that comes before it

> +	 */
> +	unsigned int num_queues_with_pending_reqs_in_root;

Why using two counters?  I mean, couldn't you simply count also the
root group in num_groups_with_pending_reqs?

> 	/*
> 	 * Per-class (RT, BE, IDLE) number of bfq_queues containing
> 	 * requests (including the queue in service, even if it is
> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
> index 7a462df71f68..188c8f907219 100644
> --- a/block/bfq-wf2q.c
> +++ b/block/bfq-wf2q.c
> @@ -946,6 +946,29 @@ static void bfq_update_fin_time_enqueue(struct bfq_entity *entity,
> 	bfq_active_insert(st, entity);
> }
> 
> +static void bfq_update_groups_with_pending_reqs(struct bfq_entity *entity)
> +{
> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
> +	struct bfq_queue *bfqq = bfq_entity_to_bfqq(entity);
> +

why do you introduce an extra variable bfqq, instead of doing as in
the original version of the code?  In addition, you remove the comment
/* bfq_group */

Thanks,
Paolo

> +	if (bfqq) {
> +		if (!entity->parent && !entity->in_groups_with_pending_reqs) {
> +			entity->in_groups_with_pending_reqs = true;
> +			bfqq->bfqd->num_queues_with_pending_reqs_in_root++;
> +		}
> +	} else {
> +		if (!entity->in_groups_with_pending_reqs) {
> +			struct bfq_group *bfqg =
> +				container_of(entity, struct bfq_group, entity);
> +			struct bfq_data *bfqd = bfqg->bfqd;
> +
> +			entity->in_groups_with_pending_reqs = true;
> +			bfqd->num_groups_with_pending_reqs++;
> +		}
> +	}
> +#endif
> +}
> +
> /**
>  * __bfq_activate_entity - handle activation of entity.
>  * @entity: the entity being activated.
> @@ -999,19 +1022,7 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
> 		entity->on_st_or_in_serv = true;
> 	}
> 
> -#ifdef CONFIG_BFQ_GROUP_IOSCHED
> -	if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
> -		struct bfq_group *bfqg =
> -			container_of(entity, struct bfq_group, entity);
> -		struct bfq_data *bfqd = bfqg->bfqd;
> -
> -		if (!entity->in_groups_with_pending_reqs) {
> -			entity->in_groups_with_pending_reqs = true;
> -			bfqd->num_groups_with_pending_reqs++;
> -		}
> -	}
> -#endif
> -
> +	bfq_update_groups_with_pending_reqs(entity);
> 	bfq_update_fin_time_enqueue(entity, st, backshifted);
> }
> 
> -- 
> 2.31.1
>