Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2 1/1] blk-mq: fill header with kernel-doc
To:     Gabriel Krisman Bertazi <krisman@collabora.com>
Cc:     =?UTF-8?Q?Andr=c3=a9_Almeida?= <andrealmeid@collabora.com>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        axboe@kernel.dk, kernel@collabora.com
References: <20191008001416.12656-1-andrealmeid@collabora.com>
 <854l0j19go.fsf@collabora.com> <6aa48cd2-5f23-a4be-f777-d65bf755a976@acm.org>
 <85zhibyt14.fsf@collabora.com>
From:   Bart Van Assche <bvanassche@acm.org>
Message-ID: <86de2c88-5812-4a87-b5d8-1b7b1808d013@acm.org>
Date:   Tue, 8 Oct 2019 13:01:38 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: <85zhibyt14.fsf@collabora.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.