linux-kernel - Re: [PATCH RFC v2 6/6] blk-throtl: switch to use rq

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Date: Sat, 13 Apr 2024 10:17:51 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Tejun Heo <tj@...nel.org>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, chenhuacai@...nel.org, josef@...icpanda.com,
 jhs@...atatu.com, svenjoac@....de, raven@...maw.net, pctammela@...atatu.com,
 qde@...cy.de, zhaotianrui@...ngson.cn, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
 cgroups@...r.kernel.org, yi.zhang@...wei.com, yangerkun@...wei.com,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC v2 6/6] blk-throtl: switch to use rq_qos

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@...wei.com>
>>
>> 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.
>