Re: [PATCH -next v3 2/3] block, bfq: refactor the counting of 'num_groups_with_pending_reqs'

[yukuai (C)]

在 2022/04/27 20:49, Jan Kara 写道:
> On Wed 27-04-22 20:47:21, Yu Kuai wrote:
> > Currently, bfq can't handle sync io concurrently as long as they
> > are not issued from root group. This is because
> > 'bfqd->num_groups_with_pending_reqs > 0' is always true in
> > bfq_asymmetric_scenario().
> >
> > The way that bfqg is counted into 'num_groups_with_pending_reqs':
> >
> > Before this patch:
> >   1) root group will never be counted.
> >   2) Count if bfqg or it's child bfqgs have pending requests.
> >   3) Don't count if bfqg and it's child bfqgs complete all the requests.
> >
> > After this patch:
> >   1) root group is counted.
> >   2) Count if bfqg have at least one bfqq that is marked busy.
> >   3) Don't count if bfqg doesn't have any busy bfqqs.
> >
> > With this change, the occasion that only one group is activated can be
> > detected, and next patch will support concurrent sync io in the
> > occasion.
> >
> > This patch also rename 'num_groups_with_pending_reqs' to
> > 'num_groups_with_busy_queues'.
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Looks good. Just I think you forgot to remove in_groups_with_pending_reqs,
> which is now unused, from bfq_entity.

Will remove it in the next iteration.

Thanks,
Kuai