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

[yukuai (C)]

On 2021/08/27 1:00, Paolo Valente wrote:
> > Il giorno 6 ago 2021, alle ore 04:08, Yu Kuai <yukuai3@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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?

Hi, Paolo

Thanks for taking time reviewing these patches

I was doing this too complicated, while counting root group into
num_groups_with_pending_reqs is much easier. I'll do this in next
iteration.

Thanks
Yu Kuai

> > 	/*
> > 	 * 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
>
> .