Re: [PATCH v2 2/4] block, bfq: do not idle if only one cgroup is activated

[yukuai (C)]

On 2021/08/27 1:00, Paolo Valente wrote:
> Why do you make these extensive changes, while you can leave all the
> function unchanged and just modify the above condition to something
> like
>
> || bfqd->num_groups_with_pending_reqs > 1
> || (bfqd->num_groups_with_pending_reqs && bfqd->num_queues_with_pending_reqs_in_root)

Hi, Paolo

I was thinking that if CONFIG_BFQ_GROUP_IOSCHED is enabled, there is no
need to caculate smallest_weight, varied_queue_weights, and
multiple_classes_busy:

If we count root group into num_groups_with_pending_reqs
 - If num_groups_with_pending_reqs <= 1, idle is not needed
 - If num_groups_with_pending_reqs  > 1, idle is needed

Thus such changes can save some additional overhead.

Thanks
Yu Kuai

> In addition, I still wonder whether you can simply add also the root
> group to bfqd->num_groups_with_pending_reqs (when the root group is
> active).  This would make the design much cleaner.
>
> Thanks,
> Paolo
>
> > -#endif
> > -		;
> > +	return varied_queue_weights || multiple_classes_busy;
> > }
> >
> > /*
> > --
> > 2.31.1
>
> .