linux-kernel - Re: [PATCH 2/3] mmc: block: Limit queue size for consecutive requeues

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Date:   Fri, 18 Nov 2022 13:32:34 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     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 2/3] mmc: block: Limit queue size for consecutive requeues

On 26/10/22 10:30, Christian Löhle wrote:
> In case mmcblk relies on requeueing to fulfill block layer requests due to
> hardware or driver restricting the max_blk_count to 1 also limit the
> hardware queue size to 1 to get consecutive accesses instead of a
> round-robin on all queued reads.
> 
> See SDHCI_QUIRK_NO_MULTIBLOCK for such a restriction.
> 
> Signed-off-by: Christian Loehle <cloehle@...erstone.com>
> ---
>  drivers/mmc/core/queue.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> index fefaa901b50f..3a20f3933502 100644
> --- a/drivers/mmc/core/queue.c
> +++ b/drivers/mmc/core/queue.c
> @@ -425,6 +425,8 @@ struct gendisk *mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card)
>  	if (host->cqe_enabled && !host->hsq_enabled)
>  		mq->tag_set.queue_depth =
>  			min_t(int, card->ext_csd.cmdq_depth, host->cqe_qdepth);
> +	else if (host->max_blk_count == 1)

I suggest adding a big comment here about why this is needed.
Perhaps like the information in your cover letter email.

> +		mq->tag_set.queue_depth = 1;
>  	else
>  		mq->tag_set.queue_depth = MMC_QUEUE_DEPTH;
>  	mq->tag_set.numa_node = NUMA_NO_NODE;