linux-kernel - Re: [PATCH 0/3] mmc: Improve block layer requeueing behavior

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Message-ID: <5df2c4d5-f426-e3ea-8e6d-f772ec7091b6@intel.com>
Date:   Mon, 21 Nov 2022 10:25:44 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Bart Van Assche <bvanassche@....org>,
        Christian Löhle <CLoehle@...erstone.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Cc:     Avri Altman <Avri.Altman@....com>,
        "vincent.whitchurch@...s.com" <vincent.whitchurch@...s.com>
Subject: Re: [PATCH 0/3] mmc: Improve block layer requeueing behavior

On 18/11/22 19:27, Bart Van Assche wrote:
> On 11/18/22 02:47, Adrian Hunter wrote:
>> On 26/10/22 10:30, Christian Löhle wrote:
>>> Mmcblk relies on block layer requeueing to fulfill some requests under
>>> certain conditions. Improve the handling to get nicely ordered requests.
>>>
>>> Using the terms a bit loosely to get a point across:
>>> Current behavior for 512 blksz and max_blk_count = 1 the scenario would
>>> be as follows:
>>>
>>> - request for page 0 lba 0 to 7
>>> - request for page 1 lba 8 to 15
>>> - request for page 2 lba 16 to 23
>>> - request for page 3 lba 24 to 31
>>>
>>> mmcblk modifies data->blocks = 1 for each and requeues,
>>> this leads to:
>>>
>>> Access lba 0
>>> Access lba 8
>>> Access lba 16
>>> Access lba 24
>>> Access lba 1 (1. Requeue for page 0)
>>> Access lba 9 (1. Requeue for page 1)
>>> Access lba 17 (1. Requeue for page 2)
>>> Access lba 25 (1. Requeue for page 3)
>>> Access lba 2 (2. Requeue for page 0)
>>> ...
>>>
>>> Of course we would rather have lbas consecutive.
>>
>> Does anyone know why the block layer does not support
>> (max_hw_sectors << 9) < PAGE_SIZE ?
> 
> Hi Adrian,
> 
> Does this mean that the following patch series would not only be
> useful for UFS but also for MMC? "[PATCH 00/10] Support DMA segments
> smaller than the page size"
> (https://lore.kernel.org/linux-block/20221019222324.362705-1-bvanassche@acm.org/).

That patchset still does not allow max_hw_sectors = 1 which is
what Christian's case needs.