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From: Bart Van Assche <bvanassche@acm.org>
To: Damien Le Moal <damien.lemoal@opensource.wdc.com>,
	Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
	Avri Altman <avri.altman@wdc.com>,
	Damien Le Moal <damien.lemoal@wdc.com>
Subject: Re: [PATCH 4/8] block/mq-deadline: Only use zone locking if necessary
Date: Mon, 9 Jan 2023 15:51:28 -0800	[thread overview]
Message-ID: <7bf28b7e-7301-29b5-c610-dff04ad6337f@acm.org> (raw)
In-Reply-To: <92096c6d-fe0a-7b5b-222f-c532286c0c8b@opensource.wdc.com>

On 1/9/23 15:46, Damien Le Moal wrote:
> On 1/10/23 08:27, Bart Van Assche wrote:
>> Measurements have shown that limiting the queue depth to one for zoned
>> writes has a significant negative performance impact on zoned UFS devices.
>> Hence this patch that disables zone locking from the mq-deadline scheduler
>> for storage controllers that support pipelining zoned writes. This patch is
>> based on the following assumptions:
>> - Applications submit write requests to sequential write required zones
>>    in order.
>> - It happens infrequently that zoned write requests are reordered by the
>>    block layer.
>> - The storage controller does not reorder write requests that have been
>>    submitted to the same hardware queue. This is the case for UFS: the
>>    UFSHCI specification requires that UFS controllers process requests in
>>    order per hardware queue.
>> - The I/O priority of all pipelined write requests is the same per zone.
>> - Either no I/O scheduler is used or an I/O scheduler is used that
>>    submits write requests per zone in LBA order.
>>
>> If applications submit write requests to sequential write required zones
>> in order, at least one of the pending requests will succeed. Hence, the
>> number of retries that is required is at most (number of pending
>> requests) - 1.
> 
> But if the mid-layer decides to requeue a write request, the workqueue
> used in the mq block layer for requeuing is going to completely destroy
> write ordering as that is outside of the submission path, working in
> parallel with it... Does blk_queue_pipeline_zoned_writes() == true also
> guarantee that a write request will *never* be requeued before hitting the
> adapter/device ?

We don't need the guarantee that reordering will never happen. What we 
need is that reordering happens infrequently (e.g. less than 1% of the 
cases). This is what the last paragraph before your reply refers to. 
Maybe I should expand that paragraph.

Thanks,

Bart.


  reply	other threads:[~2023-01-09 23:51 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-09 23:27 [PATCH 0/8] Enable zoned write pipelining for UFS devices Bart Van Assche
2023-01-09 23:27 ` [PATCH 1/8] block: Document blk_queue_zone_is_seq() and blk_rq_zone_is_seq() Bart Van Assche
2023-01-09 23:36   ` Damien Le Moal
2023-01-09 23:27 ` [PATCH 2/8] block: Introduce the blk_rq_is_seq_zone_write() function Bart Van Assche
2023-01-09 23:38   ` Damien Le Moal
2023-01-09 23:52     ` Bart Van Assche
2023-01-10  9:52       ` Niklas Cassel
2023-01-10 11:54         ` Damien Le Moal
2023-01-10 12:13           ` Niklas Cassel
2023-01-10 12:41             ` Damien Le Moal
2023-01-09 23:27 ` [PATCH 3/8] block: Introduce a request queue flag for pipelining zoned writes Bart Van Assche
2023-01-09 23:27 ` [PATCH 4/8] block/mq-deadline: Only use zone locking if necessary Bart Van Assche
2023-01-09 23:46   ` Damien Le Moal
2023-01-09 23:51     ` Bart Van Assche [this message]
2023-01-09 23:56       ` Damien Le Moal
2023-01-10  0:19         ` Bart Van Assche
2023-01-10  0:32           ` Damien Le Moal
2023-01-10  0:38             ` Jens Axboe
2023-01-10  0:41               ` Jens Axboe
2023-01-10  0:44                 ` Bart Van Assche
2023-01-10  0:48                   ` Jens Axboe
2023-01-10  0:56                     ` Bart Van Assche
2023-01-10  1:03                       ` Jens Axboe
2023-01-10  1:17                         ` Bart Van Assche
2023-01-10  1:48                           ` Jens Axboe
2023-01-10  2:24                     ` Damien Le Moal
2023-01-10  3:00                       ` Jens Axboe
2023-01-09 23:27 ` [PATCH 5/8] block/null_blk: Refactor null_queue_rq() Bart Van Assche
2023-01-09 23:27 ` [PATCH 6/8] block/null_blk: Add support for pipelining zoned writes Bart Van Assche
2023-01-09 23:27 ` [PATCH 7/8] scsi: Retry unaligned " Bart Van Assche
2023-01-09 23:51   ` Damien Le Moal
2023-01-09 23:55     ` Bart Van Assche
2023-01-09 23:27 ` [PATCH 8/8] scsi: ufs: Enable zoned write pipelining Bart Van Assche
2023-01-10  9:16   ` Avri Altman
2023-01-10 17:42     ` Bart Van Assche
2023-01-10 12:23   ` Bean Huo
2023-01-10 17:41     ` Bart Van Assche

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