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Date: Tue, 8 Oct 2019 13:01:38 -0700 From: Bart Van Assche <bvanassche@....org> To: Gabriel Krisman Bertazi <krisman@...labora.com> Cc: André Almeida <andrealmeid@...labora.com>, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, axboe@...nel.dk, kernel@...labora.com Subject: Re: [PATCH v2 1/1] blk-mq: fill header with kernel-doc 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.
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