Re: [PATCH -next 10/11] block, bfq: decrease 'num_groups_with_pending_reqs' earlier

[yukuai (C)]

在 2022/04/13 19:28, Jan Kara 写道:
> On Sat 05-03-22 17:12:04, Yu Kuai wrote:
> > Currently 'num_groups_with_pending_reqs' won't be decreased when
> > the group doesn't have any pending requests, while some child group
> > still have pending requests. The decrement is delayed to when all the
> > child groups doesn't have any pending requests.
> >
> > For example:
> > 1) t1 issue sync io on root group, t2 and t3 issue sync io on the same
> > child group. num_groups_with_pending_reqs is 2 now.
> > 2) t1 stopped, num_groups_with_pending_reqs is still 2. io from t2 and
> > t3 still can't be handled concurrently.
> >
> > Fix the problem by decreasing 'num_groups_with_pending_reqs'
> > immediately upon the weights_tree removal of last bfqq of the group.
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> So I'd find the logic easier to follow if you completely removed
> entity->in_groups_with_pending_reqs and did updates of
> bfqd->num_groups_with_pending_reqs like:
>
> 	if (!bfqg->num_entities_with_pending_reqs++)
> 		bfqd->num_groups_with_pending_reqs++;
Hi,

Indeed, this is an excellent idle, and much better than the way I did.

Thanks,
Kuai

> and similarly on the remove side. And there would we literally two places
> (addition & removal from weight tree) that would need to touch these
> counters. Pretty obvious and all can be done in patch 9.
>
> 								Honza