[PATCH v2 4/7] blk-mq: Introduce blk_quiesce_queue() and blk_resume_queue()

[Bart Van Assche]

On 10/05/2016 11:14 AM, Sagi Grimberg wrote:
>> Hello Ming,
>>
>> Can you have a look at the attached patch? That patch uses an srcu read
>> lock for all queue types, whether or not the BLK_MQ_F_BLOCKING flag has
>> been set. Additionally, I have dropped the QUEUE_FLAG_QUIESCING flag.
>> Just like previous versions, this patch has been tested.
>
> Hey Bart,
>
> Do we care about the synchronization of queue_rq and/or
> blk_mq_run_hw_queue of the hctx is not stopped?
>
> I'm wandering if we can avoid introducing new barriers in the
> submission path of its not absolutely needed.

Hello Sagi,

I'm not sure whether the new blk_quiesce_queue() function is useful 
without stopping all hardware contexts first. In other words, in my view 
setting BLK_MQ_F_BLOCKING flag before calling blk_quiesce_queue() is 
sufficient and I don't think that a new QUEUE_FLAG_QUIESCING flag is 
necessary.

Bart.