On Fri 15-04-22 09:10:06, yukuai (C) wrote: > 在 2022/04/13 19:40, yukuai (C) 写道: > > 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. > > I think with this change, we can count root_group while activating bfqqs > that are under root_group, thus there is no need to modify > for_each_entity(or fake bfq_sched_data) any more. Sure, if you can make this work, it would be easier :) > The special case is that weight racing bfqqs are not inserted into > weights tree, and I think this can be handled by adding a fake > bfq_weight_counter for such bfqqs. Do you mean "weight raised bfqqs"? Yes, you are right they would need special treatment - maybe bfq_weights_tree_add() is not the best function to use for this and we should rather use insertion / removal from the service tree for maintaining num_entities_with_pending_reqs counter? I can even see we already have bfqg->active_entities so maybe we could just somehow tweak that accounting and use it for our purposes? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
