[dm-devel] [PATCH 1/5] block: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE

[Ming Lei]

On Wed, Sep 20, 2017 at 12:49 AM, Bart Van Assche
<Bart.VanAssche at wdc.com> wrote:
> On Wed, 2017-09-20 at 00:04 +0800, Ming Lei wrote:
>> Run queue at end_io is definitely wrong, because blk-mq has SCHED_RESTART
>> to do that already.
>
> Sorry but I disagree. If SCHED_RESTART is set that causes the blk-mq core to
> reexamine the software queues and the hctx dispatch list but not the requeue
> list. If a block driver returns BLK_STS_RESOURCE then requests end up on the
> requeue list. Hence the following code in scsi_end_request():

That doesn't need SCHED_RESTART, because it is requeue's
responsibility to do that,
see blk_mq_requeue_work(), which will run hw queue at the end of this func.


-- 
Ming Lei