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From: Bart Van Assche <bvanassche@acm.org>
To: Jens Axboe <axboe@kernel.dk>,
	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 16:56:33 -0800	[thread overview]
Message-ID: <31d32f69-4c14-c9be-494f-7071112073f9@acm.org> (raw)
In-Reply-To: <72092951-3de8-35a3-9e50-74cdcc9ee772@kernel.dk>

On 1/9/23 16:48, Jens Axboe wrote:
> On 1/9/23 5:44?PM, Bart Van Assche wrote:
>> On 1/9/23 16:41, Jens Axboe wrote:
>>> Or, probably better, a stacked scheduler where the bottom one can be zone
>>> away. Then we can get rid of littering the entire stack and IO schedulers
>>> with silly blk_queue_pipeline_zoned_writes() or blk_is_zoned_write() etc.
>>
>> Hi Jens,
>>
>> Isn't one of Damien's viewpoints that an I/O scheduler should not do
>> the reordering of write requests since reordering of write requests
>> may involve waiting for write requests, write request that will never
>> be received if all tags have been allocated?
> 
> It should be work conservering, it should not wait for anything. If
> there are holes or gaps, then there's nothing the scheduler can do.
> 
> My point is that the strict ordering was pretty hacky when it went in,
> and rather than get better, it's proliferating. That's not a good
> direction.

Hi Jens,

As you know one of the deeply embedded design choices in the blk-mq code 
is that reordering can happen at any time between submission of a 
request to the blk-mq code and request completion. I agree with that 
design choice.

For the use cases I'm looking at the sequential write required zone type 
works best. This zone type works best since it guarantees that data on 
the storage medium is sequential. This results in optimal sequential 
read performance.

Combining these two approaches is not ideal and I agree that the 
combination of these two approaches adds some complexity. Personally I 
prefer to add a limited amount of complexity rather than implementing a 
new block layer from scratch.

Thanks,

Bart.



  reply	other threads:[~2023-01-10  0:56 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 [this message]
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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