On 10/8/19 11:46 AM, Gabriel Krisman Bertazi wrote:
Hmm, sorry, but I'm confused. I'm sure I'm missing something simple,
since I haven't touched this in a while, so maybe you can quickly point
me in the right direction?
I see blk_mq_requeue_request() being used by device drivers to retry
requests that failed, but if I read the code correctly, the flushed
queue seems to be moved to hctx->dispatch when the device
driver returned BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE to
blk_mq_dispatch_rq_list(). I thought BLK_STS_RESOURCE was returned by
the driver on .queue_rq() to signal there was no more resources on the
hardware to service further requests.
Hi Gabriel,
The simplified version of how requests are requeued as follows:
* A block driver calls blk_mq_requeue_request().
* blk_mq_requeue_request() calls blk_mq_add_to_requeue_list()
* blk_mq_add_to_requeue_list() executes the following code:
list_add_tail(&rq->queuelist, &q->requeue_list)
* A block driver or the block layer core calls
blk_mq_kick_requeue_list() or blk_mq_delay_kick_requeue_list(). Both
functions trigger a call of blk_mq_requeue_work().
* blk_mq_requeue_work() processes q->requeue_list.
Bart.
