Re: [PATCH v4 1/2] block, bfq: counted root group into 'num_groups_with_pending_reqs'

[yukuai (C)]

On 2021/10/20 17:29, Paolo Valente wrote:
> > Il giorno 20 ott 2021, alle ore 11:20, yukuai (C) <yukuai3@xxxxxxxxxx> ha scritto:
> >
> > On 2021/10/20 16:51, Paolo Valente wrote:
> >
> > > > @@ -860,9 +870,25 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
> > > > 			     struct bfq_queue *bfqq)
> > > > {
> > > > 	struct bfq_entity *entity = bfqq->entity.parent;
> > > > +	struct bfq_sched_data *sd;
> > > > +
> > > > +	/*
> > > > +	 * If the bfq queue is in root group, the decrement of
> > > > +	 * num_groups_with_pending_reqs is performed immediately upon the
> > > > +	 * deactivation of entity.
> > > > +	 */
> > > > +	if (!entity) {
> > > > +		entity = &bfqd->root_group->entity;
> > > > +		sd = entity->my_sched_data;
> > > > +
> > > > +		if (!sd->in_service_entity)
> > > > +			bfq_clear_group_with_pending_reqs(bfqd, entity);
> > > > +
> > > > +		return;
> > > > +	}
> > > >
> > > > 	for_each_entity(entity) {
> > > > -		struct bfq_sched_data *sd = entity->my_sched_data;
> > > > +		sd = entity->my_sched_data;
> > > >
> > > > 		if (sd->next_in_service || sd->in_service_entity) {
> > > > 			/*
> > > > @@ -880,7 +906,8 @@ void bfq_weights_tree_remove(struct bfq_data *bfqd,
> > > > 		}
> > > >
> > > > 		/*
> > > > -		 * The decrement of num_groups_with_pending_reqs is
> > > > +		 * If the bfq queue is not in root group,
> > > > +		 * the decrement of num_groups_with_pending_reqs is
> > > I'm sorry if I didn't notice this before, but why do you postpone the
> > > decrement only for queues not in root group?  If I'm not missing
> > > anything, the active (i.e., with pending reqs) state of the root group
> > > is to be computed as that of ay other group.
> >
> > Hi, Paolo
> >
> > I thought if queue is in root group, then bfqq->entity.parent is NULL,
> > and such case is handled above, which is separate from previous
> > implementation for queues that are not in root group.
> >
> > Is this the wrong way to handle root group?
>
> I think that, if we want to count also the root group among the active
> ones, then the logic for tagging the root group as active must be the
> same as the other groups. Or am I missing something?

Hi, Paolo

Currently, if queue is in root group, bfqq->entity.parent is NULL, and
this makes it hard to keep the same logic.

Can we store root_group->my_entity to bfqq->entity.parent if the queue
is in root group?

Thanks,
Kuai