Re: [PATCH RFC v2 6/6] blk-throtl: switch to use rq_qos

[Yu Kuai]

Hi,

在 2024/04/13 2:11, Tejun Heo 写道:
> Hello,
>
> On Sat, Apr 06, 2024 at 04:00:59PM +0800, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > To avoid exposing blk-throttle internal implementation to general block
> > layer.
> ...
> > @@ -832,7 +832,7 @@ void submit_bio_noacct(struct bio *bio)
> >   		goto not_supported;
> >   	}
> >   
> > -	if (blk_throtl_bio(bio))
> > +	if (rq_qos_throttle_bio(q, bio))
> >   		return;
> >   	submit_bio_noacct_nocheck(bio);
> >   	return;
>
> This is a half-way conversion, right? You're adding a dedicated hook to
> rq_qos and none of the other hooks can be used by blk-throtl. Even the name,
> rq_qos_throttle_bio(), becomes a misnomer. I'm not really sure this makes
> things better or worse. It makes certain things a bit cleaner but other
> things nastier. I don't know.

Yes, the final goal is making all blk-cgroup policies modular, and this
patch use rq-qos to prevent exposing blk-throtle to block layer, like
other policies.

There is another choice that I think is feasible:

Let blk-throttle ping a policy id, and use the id to call throttle
function directly, this will require initializing the 'plid' from
blkcg_policy() during definition instead of blkcg_policy_register().

Thanks,
Kuai

> Thanks.