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Date:   Thu, 23 Mar 2023 09:19:01 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
        Ming Lei <ming.lei@redhat.com>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>
Subject: Re: [PATCH v2 3/3] block: Preserve LBA order when requeuing
Message-ID: <20230323081901.GA21977@lst.de>
References: <20230320234905.3832131-1-bvanassche@acm.org> <20230320234905.3832131-4-bvanassche@acm.org> <20230321055802.GA18078@lst.de> <6325fba6-3dac-9391-28ef-177fcae9ad0a@acm.org>
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On Tue, Mar 21, 2023 at 07:46:51AM -0700, Bart Van Assche wrote:
> On 3/20/23 22:58, Christoph Hellwig wrote:
>> On Mon, Mar 20, 2023 at 04:49:05PM -0700, Bart Van Assche wrote:
>>> When requeuing a request to a zoned block device, preserve the LBA order
>>> per zone.
>>
>> What causes this requeue?
>
> Hi Christoph,
>
> Two examples of why the SCSI core can decide to requeue a command are a 
> retryable unit attention or ufshcd_queuecommand() returning 
> SCSI_MLQUEUE_HOST_BUSY. For example, ufshcd_queuecommand() returns 
> SCSI_MLQUEUE_HOST_BUSY while clock scaling is in progress (changing the 
> frequency of the link between host controller and UFS device).

None of these should happen as the upper layers enforce a per-zone
queue depth of 1.