Re: [PATCH 2/4] block, bfq: avoid moving bfqq to it's parent bfqg

[yukuai (C)]

在 2021/12/21 18:16, Jan Kara 写道:
> On Tue 21-12-21 11:21:33, Yu Kuai wrote:
> > Moving bfqq to it's parent bfqg is pointless.
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Did you notice that this is happening often enough that the check is worth
> it? Where do we do this?

I noticed that this will happend when root group is offlined:

bfq_pd_offline
 bfq_put_async_queues
  __bfq_put_async_bfqq
   bfq_bfqq_move

I'm not sure if there are other situations. I think bfq_bfqq_move()
is not happening often itself, thus the checking won't affect
performance.

Thanks,
Kuai
> 								Honza
>
> > ---
> >   block/bfq-cgroup.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
> > index 24a5c5329bcd..0f62546a72d4 100644
> > --- a/block/bfq-cgroup.c
> > +++ b/block/bfq-cgroup.c
> > @@ -645,6 +645,11 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> >   		   struct bfq_group *bfqg)
> >   {
> >   	struct bfq_entity *entity = &bfqq->entity;
> > +	struct bfq_group *old_parent = bfq_group(bfqq);
> > +
> > +	/* No point to move bfqq to the same group */
> > +	if (old_parent == bfqg)
> > +		return;
> >   
> >   	/*
> >   	 * Get extra reference to prevent bfqq from being freed in
> > @@ -666,7 +671,7 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
> >   		bfq_deactivate_bfqq(bfqd, bfqq, false, false);
> >   	else if (entity->on_st_or_in_serv)
> >   		bfq_put_idle_entity(bfq_entity_service_tree(entity), entity);
> > -	bfqg_and_blkg_put(bfqq_group(bfqq));
> > +	bfqg_and_blkg_put(old_parent);
> >   
> >   	if (entity->parent &&
> >   	    entity->parent->last_bfqq_created == bfqq)
> > --
> > 2.31.1