All of lore.kernel.org
 help / color / mirror / Atom feed
From: Damien Le Moal <damien.lemoal@opensource.wdc.com>
To: Bart Van Assche <bvanassche@acm.org>, 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: Tue, 10 Jan 2023 09:32:32 +0900	[thread overview]
Message-ID: <681a991f-e09a-eeb6-805a-ee807250c399@opensource.wdc.com> (raw)
In-Reply-To: <b72e484c-2985-a755-b0e1-e9ccd93cfc3b@acm.org>

On 1/10/23 09:19, Bart Van Assche wrote:
> On 1/9/23 15:56, Damien Le Moal wrote:
>> But my point is that if a request goes through the block layer requeue, it
>> will be out of order, and will be submitted out of order again, and will
>> fail again. Unless you stall dispatching, wait for all requeues to come
>> back in the scheduler, and then start trying again, I do not see how you
>> can guarantee that retrying the unaligned writes will ever succeed.
>>
>> I am talking in the context of host-managed devices here.
> 
> Hi Damien,
> 
> How about changing the NEEDS_RETRY in patch 7/8 into another value than 
> SUCCESS, NEEDS_RETRY or ADD_TO_MLQUEUE? That will make the SCSI core 
> wait until all pending commands have finished before it starts its error 
> handling strategy and before it requeues any pending commands.

Considering a sequence of sequential write requests, the request can be in:
1) The scheduler
2) The dispatch queue (out of the scheduler)
3) In the requeue list, waiting to be put back in the scheduler
4) in-flight being processed for dispatch by the scsi mid-layer & scsi
disk driver
5) being processed by the driver
6) dispatched to the device already

Requeue back to the scheduler can happen anywhere after (2) up to (5)
(would need to check again to be 100% sure though). So I do not see how
changes to the scsi layer only, adding a new state, can cover all possible
cases resulting at some point to come back to a clean ordering. But if you
have ideas to prove me wrong, I will be happy to review that :)

So far, the only thing that I think could work is: stall everything and
put back all write requests in the scheduler, and restart dispatching.
That will definitively have a performance impact. How does that compare to
the zone write locking performance impact, I am not sure...

It may be way simpler to rely on:
1) none scheduler
2) some light re-ordering of write requests in the driver itself to avoid
any requeue to higher level (essentially, handle requeueing in the driver
itself).

> 
> Thanks,
> 
> Bart.

-- 
Damien Le Moal
Western Digital Research


  reply	other threads:[~2023-01-10  0:32 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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=681a991f-e09a-eeb6-805a-ee807250c399@opensource.wdc.com \
    --to=damien.lemoal@opensource.wdc.com \
    --cc=avri.altman@wdc.com \
    --cc=axboe@kernel.dk \
    --cc=bvanassche@acm.org \
    --cc=damien.lemoal@wdc.com \
    --cc=jaegeuk@kernel.org \
    --cc=linux-block@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.