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From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <bvanassche@acm.org>,
	Damien Le Moal <damien.lemoal@opensource.wdc.com>
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 18:48:03 -0700	[thread overview]
Message-ID: <8f653339-cd1a-5078-d34f-7b6951baf64a@kernel.dk> (raw)
In-Reply-To: <f47f32d8-92a3-b7d5-a462-d34da9263d34@acm.org>

On 1/9/23 6:17?PM, Bart Van Assche wrote:
> On 1/9/23 17:03, Jens Axboe wrote:
>> Because I'm really not thrilled to see the addition of various "is this
>> device ordered" all over the place, and now we are getting "is this
>> device ordered AND pipelined". Do you see what I mean? It's making
>> things _worse_, not better, and we really should be making it better
>> rather than pile more stuff on top of it.
> 
> Hi Jens,
> 
> I agree with you that the additional complexity is unfortunate.
> 
> For most zoned storage use cases a queue depth above one is not an
> option if the zoned device expects zoned write commands in LBA order.
> ATA controllers do not support preserving the command order.
> Transports like NVMeOF do not support preserving the command order
> either. UFS is an exception. The only use case supported by the UFS
> specification is a 1:1 connection between UFS controller and UFS
> device with a link with a low BER between controller and device. UFS
> controllers must preserve the command order per command queue. I think
> this context is well suited for pipelining zoned write commands.

But it should not matter, if the scheduler handles it, and requeues are
ordered correctly. If the queue depth isn't known at init time, surely
we'd get a retry condition on submitting a request if it can't accept
another one. That'd trigger a retry, and the retry should be the first
one submitted when the device can accept another one.

Any setup that handles queue depth > 1 will do just fine at 1 as well.

-- 
Jens Axboe


  reply	other threads:[~2023-01-10  1:48 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
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 [this message]
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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