Re: [RFC V5 01/16] blk: make the whole blk_mq_submit_bio under q_usage_counter

[Wang Jianchao]

On 2022/2/24 9:38 下午, Christoph Hellwig wrote:
> On Thu, Feb 24, 2022 at 05:06:39PM +0800, Wang Jianchao (Kuaishou) wrote:
>> This is to protect the rqos list against the rqos open/close. We
>> need to drain all of the caller of blk_mq_submit_bio() before
>> we can operate the rqos list.
> 
> This means ever I/O now has to d an extra refcount roundtrip.

If we want to save cpu cycles for the very fast device, why not introduce
another blk_mq_submit_bio_fast() which can reduce the code drastically.

Thanks
Jianchao